bash completion with colour hints

Hi Shawn

I only recently found the __git_ps1 function, but it wasn't directly 
able to replace my own contraption. I've modified the version I found 
after installing bash-completion in debian 6.

The patch is attached, it contains an escape character, so it is hard to 
include in plain text. I've gzipped it for convenience...

This is only a first step, I had a hard time figuring out what exactly 
the one-letter variables were doing (and still a bit unclear), so I'm 
sure this can be improved!

Anyway, the functionality of this patch is to show the output in green 
if the repo is up to date and red or other colours if it isn't.

Cheers

Simon