Fix atmosphere disconnect handling

Only remove session attribute _after_ the client is retrieved from the session and sent the `Disconnected` message.
Also removing the pointless first `isCancelled` check.
Conflicts:
	atmosphere/src/main/scala/org/scalatra/atmosphere/ScalatraAtmosphereHandler.scala
Allow Accept-Encoding header to be a list
Remove unused import
This should allow using scalate with i18n support in ScalatraFilter as well as in ScalatraServlet.
On the second thought this should do the trick even better.
Upgrade to Scalaz 7.0.4.