Configure terminal Emacs as default editor

* Setting ALTERNATE_EDITOR="" tells emacsclient to run the
  default ("emacs --daemon")
Configure gpg to work with gpg-agent

* Assuming gpg-agent has been started (through launchd or similar) load
  its environment variables from a temporary file.
* GPG_TTY needs to be set to the current tty or pinentry won't prompt
  for passwords