linux users should be able to use gpg2 if they want

[grant-olson]

On linux, gnupg 2.0 is usually installed as gpg2, and gpg points to gpg 1.4. Users should be able to somehow specify which gpg executable they want to use.

[grant-olson]

This will also be needed if we try to install a fallback version of gpg for windows users.

We'll also need to be able to hook into gpg_status_parser