commit: save commit message so it's not destroyed by rollback.
(
issue1635)
Rationale: if a pretxncommit hook rejects this commit, the transaction
is rolled back and the user's commit message is irrevocably lost.
So save a copy in .hg/last-message.txt, just in case. Also handy if
the user deliberately rolls back a commit in order to amend it.
adding a
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
committer test 0 0
revision 0
branch default
adda