Fix JUnitShell/etc so it doesn't rely on the user agent to identify different
sessions, but instead sets a session cookie.  This fixes two instances/tabs
of the same browser as well as connections via proxies.

Patch by: scottb
Review by: jat


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7153 8db76d5a-ed1c-0410-87a9-c151d255dfc7