Mute errors when hitting Ctrl-C and improve compatibility with aliases

1. Mute errors when hitting Ctrl-C. Now if you hit Ctrl-C on a prompt (as I do constantly) there will be no errors.
2. Improve compatbility with aliases. By calling `command git` instead of `git`, we ensure that aliases and wrappers are skipped to improve performance. I did this for better compatbility with [hub](https://github.com/defunkt/hub).