Assorted small issues with gwt2-1.8

[markerikson]

Ran into a couple problems upgrading from my personal tweaked version of 1.3 to version 1.8:

• Commands.py: lines 87 and 90 are "if not gwt_path", but gwt_path has already been set to "notset". Both need to be changed to "if gwt_path == 'notset' ".
• When the Play app has been compiled to a .WAR and is running under JBoss, every RPC call fails because the Java Stream provided in Play's request.body doesn't allow being read multiple times, but gwt2-1.8 calls IO.readContentAsString(request.body) in several places. I was able to work around this by calling that once in GWTController, then modifying GWTController.invoke()/invokeAsync() and GWTInvoker() to each take a "String body" parameter.