git-revert with conflicts to behave as git-merge with conflicts

git-revert with conflicts to behave as git-merge with conflicts

In a busy project, reverting a commit almost always results
in a conflict between one or more files (depending on the
commit being reverted).  It is useful to record this
conflict in the commit-to-be message of the resulting commit
(after the resolve).  The process now becomes:

git-revert <SHA-1>
<git complains and prints failed automatic>
<user manually resolves>
git-update-index <resolved files>
git-commit -s

And the commit message is now a merge of the revert commit
message and the conflict commit message, giving the user a
chance to edit it or add more information:

Signed-off-by: Luben Tuikov <ltuikov@yahoo.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>