patchbomb: add a 'patchbomb.intro' option

This option allows the user to control the default behavior for
including an introduction message. This avoids having to tirelessly
skip the intro for people contributing to Mercurial.

The three possibles values are:
- always,
- auto (default, current behavior),
- never.

I was thinking of ("true", "false", "") (empty value being auto) but I ruled it
out as too confusing.

This new config option reuses the pre-existing 'patchbomb' section.

hgext/patchbomb.py

@@ -43,6 +43,15 to be a sendmail compatible mailer or fi
 that the patchbomb extension can automatically send patchbombs
 directly from the commandline. See the [email] and [smtp] sections in
 hgrc(5) for details.
+
+You can control the default inclusion of an introduction message with the
+``patchbomb.intro`` configuration option. The configuration is always
+overwritten by command line flags like --intro and --desc::
+
+  [patchbomb]
+  intro=auto   # include introduction message if more than 1 patch (default)
+  intro=never  # never include an introduction message
+  intro=always # always include an introduction message
 '''
 
 import os, errno, socket, tempfile, cStringIO
@@ -66,9 +75,23 def prompt(ui, prompt, default=None, res
         prompt += ' [%s]' % default
     return ui.prompt(prompt + rest, default)
 
-def introwanted(opts, number):
+def introwanted(ui, opts, number):
     '''is an introductory message apparently wanted?'''
-    return number > 1 or opts.get('intro') or opts.get('desc')
+    introconfig = ui.config('patchbomb', 'intro', 'auto')
+    if opts.get('intro') or opts.get('desc'):
+        intro = True
+    elif introconfig == 'always':
+        intro = True
+    elif introconfig == 'never':
+        intro = False
+    elif introconfig == 'auto':
+        intro = 1 < number
+    else:
+        ui.write_err(_('warning: invalid patchbomb.intro value "%s"\n')
+                     % introconfig)
+        ui.write_err(_('(should be one of always, never, auto)\n'))
+        intro = 1 < number
+    return intro
 
 def makepatch(ui, repo, patchlines, opts, _charsets, idx, total, numbered,
               patchname=None):
@@ -287,7 +310,7 def _getpatchmsgs(repo, sender, patches,
              % len(patches))
 
     # build the intro message, or skip it if the user declines
-    if introwanted(opts, len(patches)):
+    if introwanted(ui, opts, len(patches)):
         msg = _makeintro(repo, sender, patches, **opts)
         if msg:
             msgs.append(msg)
@@ -407,7 +430,9 def patchbomb(ui, repo, *revs, **opts):
     for each patchbomb message, so you can verify everything is alright.
 
     In case email sending fails, you will find a backup of your series
-    introductory message in ``.hg/last-email.txt``.
+    introductory message in ``.hg/last-email.txt``. The inclusion the
+    introduction can also be control using the ``patchbomb.intro`` option. (see
+    hg help patchbomb for details)
 
     Examples::
 

tests/test-patchbomb.t

@@ -2663,4 +2663,127 dest#branch URIs:
   +d
   
 
-  $ cd ..
+Test introduction configuration
+=================================
+
+  $ echo '[patchbomb]' >> $HGRCPATH
+
+"auto" setting
+----------------
+
+  $ echo 'intro=auto' >> $HGRCPATH
+
+single rev
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '10' | grep "Write the introductory message for the patch series."
+  [1]
+
+single rev + flag
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '10' --intro | grep "Write the introductory message for the patch series."
+  Write the introductory message for the patch series.
+
+
+Multi rev
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '9::' | grep "Write the introductory message for the patch series."
+  Write the introductory message for the patch series.
+
+"never" setting
+-----------------
+
+  $ echo 'intro=never' >> $HGRCPATH
+
+single rev
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '10' | grep "Write the introductory message for the patch series."
+  [1]
+
+single rev + flag
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '10' --intro | grep "Write the introductory message for the patch series."
+  Write the introductory message for the patch series.
+
+
+Multi rev
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '9::' | grep "Write the introductory message for the patch series."
+  [1]
+
+Multi rev + flag
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '9::' --intro | grep "Write the introductory message for the patch series."
+  Write the introductory message for the patch series.
+
+"always" setting
+-----------------
+
+  $ echo 'intro=always' >> $HGRCPATH
+
+single rev
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '10' | grep "Write the introductory message for the patch series."
+  Write the introductory message for the patch series.
+
+single rev + flag
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '10' --intro | grep "Write the introductory message for the patch series."
+  Write the introductory message for the patch series.
+
+
+Multi rev
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '9::' | grep "Write the introductory message for the patch series."
+  Write the introductory message for the patch series.
+
+Multi rev + flag
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '9::' --intro | grep "Write the introductory message for the patch series."
+  Write the introductory message for the patch series.
+
+bad value setting
+-----------------
+
+  $ echo 'intro=mpmwearaclownnose' >> $HGRCPATH
+
+single rev
+
+  $ hg email --date '1980-1-1 0:1' -n -t foo -s test -r '10'
+  From [test]: test
+  this patch series consists of 1 patches.
+  
+  warning: invalid patchbomb.intro value "mpmwearaclownnose"
+  (should be one of always, never, auto)
+  Cc: 
+  
+  displaying [PATCH] test ...
+  Content-Type: text/plain; charset="us-ascii"
+  MIME-Version: 1.0
+  Content-Transfer-Encoding: 7bit
+  Subject: [PATCH] test
+  X-Mercurial-Node: 3b6f1ec9dde933a40a115a7990f8b320477231af
+  X-Mercurial-Series-Index: 1
+  X-Mercurial-Series-Total: 1
+  Message-Id: <3b6f1ec9dde933a40a11*> (glob)
+  X-Mercurial-Series-Id: <3b6f1ec9dde933a40a11.*> (glob)
+  User-Agent: Mercurial-patchbomb/* (glob)
+  Date: Tue, 01 Jan 1980 00:01:00 +0000
+  From: test
+  To: foo
+  
+  # HG changeset patch
+  # User test
+  # Date 5 0
+  #      Thu Jan 01 00:00:05 1970 +0000
+  # Branch test
+  # Node ID 3b6f1ec9dde933a40a115a7990f8b320477231af
+  # Parent  2f9fa9b998c5fe3ac2bd9a2b14bfcbeecbc7c268
+  dd
+  
+  diff -r 2f9fa9b998c5 -r 3b6f1ec9dde9 d
+  --- a/d	Thu Jan 01 00:00:04 1970 +0000
+  +++ b/d	Thu Jan 01 00:00:05 1970 +0000
+  @@ -1,1 +1,2 @@
+   d
+  +d
+