backout: use "getcommiteditor()" instead of explicit editor choice

This patch also enhances "test-backout.t", because "hg backout" hasn't
been explicitly tested around editor invocation and '--edit' option.

mercurial/commands.py

@@ -488,11 +488,11 b' def backout(ui, repo, node=None, rev=Non'
 
 
         def commitfunc(ui, repo, message, match, opts):
-            e = cmdutil.commiteditor
+            e = cmdutil.getcommiteditor()
             if not message:
                 # we don't translate commit messages
                 message = "Backed out changeset %s" % short(node)
-                e = cmdutil.commitforceeditor
+                e = cmdutil.getcommiteditor(edit=True)
             return repo.commit(message, opts.get('user'), opts.get('date'),
                                match, editor=e)
         newnode = cmdutil.commit(ui, repo, commitfunc, [], opts)

tests/test-backout.t

@@ -11,6 +11,8 b' should complain'
   [255]
 
 basic operation
+(this also tests that editor is invoked if the commit message is not
+specified explicitly)
 
   $ echo a > a
   $ hg commit -d '0 0' -A -m a
@@ -18,8 +20,19 b' basic operation'
   $ echo b >> a
   $ hg commit -d '1 0' -m b
 
-  $ hg backout -d '2 0' tip --tool=true
+  $ hg status --rev tip --rev "tip^1"
+  M a
+  $ HGEDITOR=cat hg backout -d '2 0' tip --tool=true
   reverting a
+  Backed out changeset a820f4f40a57
+  
+  
+  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
+  HG: Leave message empty to abort commit.
+  HG: --
+  HG: user: test
+  HG: branch 'default'
+  HG: changed a
   changeset 2:2929462c3dff backs out changeset 1:a820f4f40a57
   $ cat a
   a
@@ -31,6 +44,8 b' basic operation'
   update: (current)
 
 file that was removed is recreated
+(this also tests that editor is not invoked if the commit message is
+specified explicitly)
 
   $ cd ..
   $ hg init remove
@@ -43,7 +58,7 b' file that was removed is recreated'
   $ hg rm a
   $ hg commit -d '1 0' -m b
 
-  $ hg backout -d '2 0' tip --tool=true
+  $ HGEDITOR=cat hg backout -d '2 0' tip --tool=true -m "Backed out changeset 76862dcce372"
   adding a
   changeset 2:de31bdc76c0d backs out changeset 1:76862dcce372
   $ cat a