Fix for issue #361

Add quick sanity check at start of state, do not attempt to do anything unless salt.gitfs.gitpython exists to check for install_from_source within

salt/gitfs/gitpython.sls

 {% from "salt/map.jinja" import salt_settings with context %}
 
+{% if 'gitfs' in salt_settings and 'gitpython' in salt_settings.gitfs %}
+
 {% if salt_settings.gitfs.gitpython.install_from_source %}
 
 GitPython:
     - name: {{ salt_settings.python_git }}
 
 {% endif %}
+
+{% endif %}