make session attribute/instance accessible via WorkspaceBuilder class

Author: tony

CHANGES

@@ -19,6 +19,8 @@ Here you can find the recent changes to tmuxp.
   detach it.
 - [cli] tmux 1.8  ``set-option`` / ``set-window-options`` command
   ``target-window`` fix.
+- [internal] :class:`WorkspaceBuilder` now has ``.session`` attribute accessible
+  publicly.
 
 2013-10-28
 ----------

tmuxp/workspacebuilder.py

@@ -122,6 +122,8 @@ def build(self, session=None):
 
             assert(self.sconf['session_name'] == session.get('session_name'))
 
+        self.session = session
+
         assert(isinstance(session, Session))
         if 'options' in self.sconf and isinstance(self.sconf['options'], dict):
             for key, val in self.sconf['options'].items():