This patch introduces a prepare-commit-msg hook that appends a ChangeLog
skeleton to a commit message when the GCC_FORCE_MKLOG environment variable
is set, and a 'git commit-mklog' command set that variable while running
'git commit'.
contrib/ChangeLog:
* prepare-commit-msg: New file.
* gcc-git-customization.sh: Install it. Add commit-mklog alias.
* mklog.py: Add new option -c which appends
to a ChangeLog file.