Restore assignment of @project ivar in TextBuffer

Because TextBuffers need a reference to `project` during deserialization,
and because the project global deserializes text buffers while it itself
is being deserialized (which happens before the global is actually
assigned), we have to pass a project reference into TextBuffer. This is
really annoying and makes me want to store the references to open buffers 
elsewhere. But for now it's the only way to break the circularity.

src/app/text-buffer.coffee

@@ -33,12 +33,13 @@ class TextBuffer
   # initialText - A {String} setting the starting text
   constructor: (optionsOrState={}, params={}) ->
     if optionsOrState instanceof telepath.Document
+      {@project} = params
       @state = optionsOrState
       @text = @state.get('text')
       filePath = @state.get('relativePath')
       @id = @state.get('id')
     else
-      {filePath, initialText} = optionsOrState
+      {@project, filePath, initialText} = optionsOrState
       @text = site.createDocument(initialText, shareStrings: true) if initialText
       @id = guid.create().toString()
       @state = site.createDocument
@@ -47,7 +48,7 @@ class TextBuffer
         version: @constructor.version
 
     if filePath
-      @setPath(project.resolve(filePath))
+      @setPath(@project.resolve(filePath))
       if @text
         @updateCachedDiskContents()
       else
@@ -74,7 +75,7 @@ class TextBuffer
     unless @destroyed
       @file?.off()
       @destroyed = true
-      project?.removeBuffer(this)
+      @project?.removeBuffer(this)
 
   retain: ->
     @refcount++
@@ -156,7 +157,7 @@ class TextBuffer
     @state.get('relativePath')
 
   setRelativePath: (relativePath) ->
-    @setPath(project.resolve(relativePath))
+    @setPath(@project.resolve(relativePath))
 
   # Sets the path for the file.
   #
@@ -168,7 +169,7 @@ class TextBuffer
     @file = new File(path)
     @file.read() if @file.exists()
     @subscribeToFile()
-    @state.set('relativePath', project.relativize(path))
+    @state.set('relativePath', @project.relativize(path))
     @trigger "path-changed", this
 
   # Retrieves the current buffer's file extension.
@@ -593,7 +594,7 @@ class TextBuffer
   checkoutHead: ->
     path = @getPath()
     return unless path
-    project.getRepo()?.checkoutHead(path)
+    @project.getRepo()?.checkoutHead(path)
 
   # Checks to see if a file exists.
   #