Make project's Git repository a window global

This allows it to operate independently of the
project and mirror the availability of the root view
and project.

src/app/window.coffee

@@ -91,6 +91,7 @@ window.handleWindowEvents = ->
 window.buildProjectAndRootView = ->
   RootView = require 'root-view'
   Project = require 'project'
+  Git = require 'git'
 
   pathToOpen = atom.getPathToOpen()
   windowState = atom.getRootViewStateForPath(pathToOpen) ? {}
@@ -102,6 +103,11 @@ window.buildProjectAndRootView = ->
 
   $(rootViewParentSelector).append(rootView)
 
+  window.git = Git.open(project.getPath())
+  project.on 'path-changed', ->
+    window.git?.destroy()
+    window.git = Git.open(project.getPath())
+
 window.stylesheetElementForId = (id) ->
   $("head style[id='#{id}']")