Don't need /usr/local/share/python any more.

Homebrew used to require /usr/local/share/python on the $PATH, but it
doesn't any more. Remove it.
Add Git branch to prompt.
Try new colour scheme: magenta hostname.
Use shorter directory path.

Now that I'm putting Git branches on the command line, I need to recover
some columns!
Add GitGutter to .gvimrc.