Merge branch 'mn/send-email-works-with-credential'

Merge branch 'mn/send-email-works-with-credential'

Hooks the credential system to send-email.

* mn/send-email-works-with-credential:
  git-send-email: use git credential to obtain password
  Git.pm: add interface for git credential command
  Git.pm: allow pipes to be closed prior to calling command_close_bidi_pipe
  Git.pm: refactor command_close_bidi_pipe to use _cmd_close
  Git.pm: fix example in command_close_bidi_pipe documentation
  Git.pm: allow command_close_bidi_pipe to be called as method