Merge branch 'bc/gpg-sign-everywhere'

Merge branch 'bc/gpg-sign-everywhere'

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