make mercurial look in more places for config files.

now it searches <install dir>/etc/mercurial, /etc/mercurial, and user
hgrc.

this allows site-wide configuration to be shared over automounted nfs
partition, instead of chenging on every system.  option of having local
configuration on every system remains.

old code for searching /etc/mercurial/hgrc.d never worked, this code
is tested and works.

doc/hgrc.5.txt

@@ -15,26 +15,38 b' aspects of its behaviour.'
 FILES
 -----
 
-Mercurial reads configuration data from up to three files, if they
-exist.  The names of these files depend on the system on which
-Mercurial is installed.
+Mercurial reads configuration data from several files, if they exist.
+The names of these files depend on the system on which Mercurial is
+installed.
 
+(Unix)    <install-root>/etc/mercurial/hgrc.d/*.rc::
+(Unix)    <install-root>/etc/mercurial/hgrc::
+    Per-installation configuration files, searched for in the
+    directory where Mercurial is installed.  For example, if installed
+    in /shared/tools, Mercurial will look in
+    /shared/tools/etc/mercurial/hgrc.  Options in these files apply to
+    all Mercurial commands executed by any user in any directory.
+
+(Unix)    /etc/mercurial/hgrc.d/*.rc::
 (Unix)    /etc/mercurial/hgrc::
 (Windows) C:\Mercurial\Mercurial.ini::
-    Options in this global configuration file apply to all Mercurial
-    commands executed by any user in any directory.
+    Per-system configuration files, for the system on which Mercurial
+    is running.  Options in these files apply to all Mercurial
+    commands executed by any user in any directory.  Options in these
+    files override per-installation options.
 
 (Unix)    $HOME/.hgrc::
 (Windows) C:\Documents and Settings\USERNAME\Mercurial.ini
-    Per-user configuration options that apply to all Mercurial commands,
-    no matter from which directory they are run.  Values in this file
-    override global settings.
+    Per-user configuration file, for the user running Mercurial.
+    Options in this file apply to all Mercurial commands executed by
+    any user in any directory.  Options in this file override
+    per-installation and per-system options.
 
 (Unix, Windows) <repo>/.hg/hgrc::
     Per-repository configuration options that only apply in a
     particular repository.  This file is not version-controlled, and
-    will not get transferred during a "clone" operation.  Values in
-    this file override global and per-user settings.
+    will not get transferred during a "clone" operation.  Options in
+    this file override options in all other configuration files.
 
 SYNTAX
 ------

mercurial/util.py

@@ -13,7 +13,7 b' platform-specific details from the core.'
 import os, errno
 from i18n import gettext as _
 from demandload import *
-demandload(globals(), "re cStringIO shutil popen2 tempfile threading time")
+demandload(globals(), "re cStringIO shutil popen2 sys tempfile threading time")
 
 def pipefilter(s, cmd):
     '''filter string S through command CMD, returning its output'''
@@ -483,12 +483,18 b" if os.name == 'nt':"
 else:
     nulldev = '/dev/null'
 
-    hgrcd = '/etc/mercurial/hgrc.d'
-    hgrcs = []
-    if os.path.isdir(hgrcd):
-        hgrcs = [f for f in os.listdir(hgrcd) if f.endswith(".rc")]
-    rcpath = map(os.path.normpath, hgrcs +
-                 ['/etc/mercurial/hgrc', os.path.expanduser('~/.hgrc')])
+    def rcfiles(path):
+        rcs = [os.path.join(path, 'hgrc')]
+        rcdir = os.path.join(path, 'hgrc.d')
+        try:
+            rcs.extend([os.path.join(rcdir, f) for f in os.listdir(rcdir)
+                        if f.endswith(".rc")])
+        except OSError, inst: pass
+        return rcs
+    rcpath = rcfiles(os.path.dirname(sys.argv[0]) + '/../etc/mercurial')
+    rcpath.extend(rcfiles('/etc/mercurial'))
+    rcpath.append(os.path.expanduser('~/.hgrc'))
+    rcpath = [os.path.normpath(f) for f in rcpath]
 
     def parse_patch_output(output_line):
         """parses the output produced by patch and returns the file name"""