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/buffer.coffee

@@ -419,12 +419,10 @@ class Buffer
         return match[0][0] != '\t'
     undefined
 
-  getRepo: -> @project?.repo
-
   checkoutHead: ->
     path = @getPath()
     return unless path
-    if @getRepo()?.checkoutHead(path)
+    if git?.checkoutHead(path)
       @trigger 'git-status-changed'
 
   scheduleStoppedChangingEvent: ->

src/app/project.coffee

@@ -7,7 +7,6 @@ EditSession = require 'edit-session'
 EventEmitter = require 'event-emitter'
 Directory = require 'directory'
 ChildProcess = require 'child-process'
-Git = require 'git'
 
 module.exports =
 class Project
@@ -35,8 +34,6 @@ class Project
     grammarOverridesByPath: @grammarOverridesByPath
 
   destroy: ->
-    @repo?.destroy()
-    @repo = null
     editSession.destroy() for editSession in @getEditSessions()
 
   addGrammarOverrideForPath: (path, grammar) ->
@@ -60,10 +57,8 @@ class Project
     if path?
       directory = if fs.isDirectory(path) then path else fs.directory(path)
       @rootDirectory = new Directory(directory)
-      @repo = Git.open(path)
     else
       @rootDirectory = null
-      @repo = null
 
     @trigger "path-changed"
 
@@ -85,7 +80,7 @@ class Project
     @ignoreRepositoryPath(path)
 
   ignoreRepositoryPath: (path) ->
-    config.get("core.hideGitIgnoredFiles") and @repo?.isPathIgnored(fs.join(@getPath(), path))
+    config.get("core.hideGitIgnoredFiles") and git?.isPathIgnored(fs.join(@getPath(), path))
 
   resolve: (filePath) ->
     filePath = fs.join(@getPath(), filePath) unless filePath[0] == '/'

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}']")