add support for cookies in the websocket

if cookies are used for session handling, please note that you have to persist your session manually.
something like ```self.app.save_session(session, make_response(""))``` after messages are received does the trick.

flask_sockets.py

@@ -1,6 +1,8 @@
 # -*- coding: utf-8 -*-
 from werkzeug.routing import Map, Rule
 from werkzeug.exceptions import NotFound
+from werkzeug.http import parse_cookie
+from flask import request
 
 def log_request(self):
     log = self.server.log
@@ -37,9 +39,13 @@ class SocketMiddleware(object):
         try:
             handler, values = adapter.match()
             environment = environ['wsgi.websocket']
+            cookie = parse_cookie(environ['HTTP_COOKIE'])
 
             with self.app.app_context():
                 with self.app.request_context(environ):
+                    # add cookie to the request to have correct session handling
+                    request.cookie = cookie
+
                     handler(environment, **values)
                     return []
         except (NotFound, KeyError):