qnew: save manually edited commit message into ".hg/last-message.txt"

Before this patch, manually edited commit message for "hg qnew -e"
isn't saved into ".hg/last-message.txt" until it is saved by
"localrepository.savecommitmessage()" in "localrepository.commit()".

This may lose such commit message, if unexpected exception is raised.

This patch saves manually edited commit message for "hg qnew -e" into
".hg/last-message.txt" just after user editing. This patch doesn't
save the message specified by -m/-l options as same as other commands.

This is the simplest implementation to fix on stable. Editing and
saving commit message should be centralized into the framework of
"localrepository.commit()" with "editor" argument in the future.

This patch uses repository wrapping class for exception raising before
saving commit message in "localrepository.commit()" easily and
certainly, because such exception requires corner case condition.

hgext/mq.py

@@ -1083,6 +1083,7 @@ class queue(object):
                         p.write("# Date %s %s\n\n" % date)
                 if util.safehasattr(msg, '__call__'):
                     msg = msg()
+                    repo.savecommitmessage(msg)
                 commitmsg = msg and msg or ("[mq]: %s" % patchfn)
                 n = newcommit(repo, None, commitmsg, user, date, match=match,
                               force=True)

tests/test-mq-qnew.t

@@ -233,3 +233,39 @@ hg headers
   use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
   abort: cannot manage merge changesets
   $ rm -r sandbox
+
+Test saving last-message.txt
+
+  $ hg init repo
+  $ cd repo
+
+  $ cat > $TESTDIR/commitfailure.py <<EOF
+  > from mercurial import util
+  > def reposetup(ui, repo):
+  >     class commitfailure(repo.__class__):
+  >         def commit(self, *args, **kwargs):
+  >             raise util.Abort('emulating unexpected abort')
+  >     repo.__class__ = commitfailure
+  > EOF
+  $ cat > .hg/hgrc <<EOF
+  > [extensions]
+  > commitfailure = $TESTDIR/commitfailure.py
+  > EOF
+
+  $ cat > $TESTDIR/editor.sh << EOF
+  > echo "==== before editing"
+  > cat \$1
+  > echo "===="
+  > echo "test saving last-message.txt" >> \$1
+  > EOF
+
+  $ rm -f .hg/last-message.txt
+  $ HGEDITOR="sh $TESTDIR/editor.sh" hg qnew -e patch
+  ==== before editing
+  ====
+  abort: emulating unexpected abort
+  [255]
+  $ cat .hg/last-message.txt
+  test saving last-message.txt
+
+  $ cd ..