Merge branch 'rebase-i-comment-squash' into jk/pu

* branch rebase-i-comment-squash:
  rebase -i: comment first line of autosquashed message

Comment out the first line of a "!squash" commit when generating a
commit message in git-rebase.

Merged to jk/pu on 2013-03-30.  Dogfooding for a while to see if
this is a sensible change.