histedit: allow "-" as a command file

When "-" is specified as a command file, we read rules from stdin. Alter a
single test to demo the behavior, but most of them could benefit from this.

There is minor change in test output resulting from the fact we no
longer change log messages.

hgext/histedit.py

@@ -143,6 +143,7 b' try:'
 except ImportError:
     import pickle
 import os
+import sys
 
 from mercurial import cmdutil
 from mercurial import discovery
@@ -515,7 +516,10 b' def histedit(ui, repo, *parent, **opts):'
             f.write(rules)
             f.close()
         else:
-            f = open(rules)
+            if rules == '-':
+                f = sys.stdin
+            else:
+                f = open(rules)
             rules = f.read()
             f.close()
         rules = [l for l in (r.strip() for r in rules.splitlines())

tests/test-histedit-fold.t

@@ -49,14 +49,12 b' log before edit'
   o  0:cb9a9f314b8b a
   
 
-  $ EDITED="$TESTTMP/editedhistory"
-  $ cat > $EDITED <<EOF
+  $ hg histedit 177f92b77385 --commands - 2>&1 <<EOF | fixbundle
   > pick e860deea161a e
   > pick 652413bf663e f
   > fold 177f92b77385 c
   > pick 055a42cdd887 d
   > EOF
-  $ HGEDITOR="cat \"$EDITED\" > " hg histedit 177f92b77385 2>&1 | fixbundle
   0 files updated, 0 files merged, 4 files removed, 0 files unresolved
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
@@ -67,9 +65,9 b' log before edit'
 
 log after edit
   $ hg logt --graph
-  @  4:7e0a290363ed d
+  @  4:9c277da72c9b d
   |
-  o  3:5e24935bad3d pick e860deea161a e
+  o  3:6de59d13424a f
   |
   o  2:ee283cb5f2d5 e
   |
@@ -138,6 +136,7 b' folded content is dropped during a merge'
   o  0:0189ba417d34 1+2+3
   
 
+  $ EDITED="$TESTTMP/editedhistory"
   $ cat > $EDITED <<EOF
   > pick 617f94f13c0f 1 +4
   > drop 888f9082bf99 2 +5