Trying out some mods to this. Seems like speed is an issue with git rev-parse
Changed find_git_branch to use rev-parse and find_git_dirty to use diff-files for speed (I think). Also removed preceding space in front of branch, and changed function syntax to to what the Git shell scripts use.
find_git_dirty: Added in check between staged and unstaged changes
Added in some redirection to check and hide error message in find_git_dirty
Merge pull request #5 from eacousineau/master

Updated to use porcelain Git commands