The run_git_commit() function already knows how to amend commits, and
with this new option, it can also clean up commit messages (i.e. strip
out commented lines). This is needed to implement rebase -i's 'fixup'
and 'squash' commands as sequencer commands.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>