Fix memory leak in GitRepository and convert to CompositeDisposables

We were calling @unsubscribe with the TextBuffer, which previously
unsubscribed from that object. The problem is that we were no longer
subscribing to that object directly, but only adding subscriptions to
that object. This caused us to never unsubscribe from buffers.

src/git-repository.coffee

@@ -1,9 +1,8 @@
 {basename, join} = require 'path'
 
 _ = require 'underscore-plus'
-{Subscriber} = require 'emissary'
 EmitterMixin = require('emissary').Emitter
-{Emitter} = require 'event-kit'
+{Emitter, Disposable, CompositeDisposable} = require 'event-kit'
 fs = require 'fs-plus'
 GitUtils = require 'git-utils'
 {deprecate} = require 'grim'
@@ -45,7 +44,6 @@ Task = require './task'
 module.exports =
 class GitRepository
   EmitterMixin.includeInto(this)
-  Subscriber.includeInto(this)
 
   @exists: (path) ->
     if git = @open(path)
@@ -75,6 +73,8 @@ class GitRepository
 
   constructor: (path, options={}) ->
     @emitter = new Emitter
+    @subscriptions = new CompositeDisposable
+
     @repo = GitUtils.open(path)
     unless @repo?
       throw new Error("No Git repository found searching path: #{path}")
@@ -88,13 +88,15 @@ class GitRepository
 
     refreshOnWindowFocus ?= true
     if refreshOnWindowFocus
-      {$} = require './space-pen-extensions'
-      @subscribe $(window), 'focus', =>
+      onWindowFocus = =>
         @refreshIndex()
         @refreshStatus()
 
+      window.addEventListener 'focus', onWindowFocus
+      @subscriptions.add new Disposable(-> window.removeEventListener 'focus', onWindowFocus)
+
     if @project?
-      @subscribe @project.eachBuffer (buffer) => @subscribeToBuffer(buffer)
+      @subscriptions.add @project.eachBuffer (buffer) => @subscribeToBuffer(buffer)
 
   # Public: Destroy this {GitRepository} object.
   #
@@ -109,7 +111,7 @@ class GitRepository
       @repo.release()
       @repo = null
 
-    @unsubscribe()
+    @subscriptions.dispose()
 
   ###
   Section: Event Subscription
@@ -403,10 +405,13 @@ class GitRepository
       if path = buffer.getPath()
         @getPathStatus(path)
 
-    @subscribe buffer.onDidSave(getBufferPathStatus)
-    @subscribe buffer.onDidReload(getBufferPathStatus)
-    @subscribe buffer.onDidChangePath(getBufferPathStatus)
-    @subscribe buffer.onDidDestroy => @unsubscribe(buffer)
+    bufferSubscriptions = new CompositeDisposable
+    bufferSubscriptions.add buffer.onDidSave(getBufferPathStatus)
+    bufferSubscriptions.add buffer.onDidReload(getBufferPathStatus)
+    bufferSubscriptions.add buffer.onDidChangePath(getBufferPathStatus)
+    bufferSubscriptions.add buffer.onDidDestroy =>
+      bufferSubscriptions.dispose()
+      @subscriptions.remove(bufferSubscriptions)
 
   # Subscribes to editor view event.
   checkoutHeadForEditor: (editor) ->