More updates, and nice functionality

Hi,

I've synchronized with the latest master (v1.8.3-rc0), and I also added a patch that I've been cooking for some time that adds nice zsh-specific functionality, similar to the _git completion from zsh.

Without compromising the speed, of course ;)

More information on the mail I sent to the git mailing list:
http://article.gmane.org/gmane.comp.version-control.git/222695