Merge branch 'jk/git-prompt'

Merge branch 'jk/git-prompt'

* jk/git-prompt:
  contrib: add credential helper for OS X Keychain
  Makefile: OS X has /dev/tty
  Makefile: linux has /dev/tty
  credential: use git_prompt instead of git_getpass
  prompt: use git_terminal_prompt
  add generic terminal prompt function
  refactor git_getpass into generic prompt function
  move git_getpass to its own source file
  imap-send: don't check return value of git_getpass
  imap-send: avoid buffer overflow

Conflicts:
	Makefile