RestirctToDirectory, Authors & gutUserHome

Hi,
I've made some changes to ungit (some time ago) and now merged them back into your most recent commit.
I hope you can use it and Integrate it into your Repository.

* RestirctToDirectory: Configration-Parameter to restrict all Filesystem related actions to a preset Path
* Authors: When used with multiple Logins this can add "--author=..." to "git commit" calls
* gutUserHome: Fallback to "/tmp" if no user home exists (when run as a daemon)

Sorry for any inconvenience this is my first pull request (I only partly know what i'am doing here) ;)
greets z.c