Preliminary implementation of setup/refresh functions
Preliminary implementation of setup/refresh functions

Added one function (setup) and an alias (refresh simply calls setup).
These functions give the developer one more way to configure the git
executable path. This also allows the user to interactively adjust the
git executable configured during runtime as these functions dynamically
update the executable path for the entire git module.

gitpython-developers/GitPython,jeblair/GitPython,gitpython-developers/gitpython,gitpython-developers/gitpython,jeblair/GitPython,gitpython-developers/GitPython