Teach "--gpg-sign" option to many commands that create commits.
* bc/gpg-sign-everywhere:
pull: add the --gpg-sign option.
rebase: add the --gpg-sign option
rebase: parse options in stuck-long mode
rebase: don't try to match -M option
rebase: remove useless arguments check
am: add the --gpg-sign option
am: parse options in stuck-long mode
git-sh-setup.sh: add variable to use the stuck-long mode
cherry-pick, revert: add the --gpg-sign option