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