Adds a __gwt_disconnected function to hosted.html, which glasses the screen and puts up a disconnect message.

This function is to be called from the GWT dev plugin.

Review by: jat

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7097 8db76d5a-ed1c-0410-87a9-c151d255dfc7