Fixing the "-bash: __git_ps1: command not found" error

Since Mac OS X installations of Git don't have "__git_ps1" included, we
need to grab .git-prompt.sh from github
(https://raw.github.com/git/git/master/contrib/completion/git-prompt.sh)
 and place it in our home directory and import this file
Merge pull request #1 from jrmsklar/Bash2Fix

Fixing the "-bash: __git_ps1: command not found" error