Fixes for accessing the resource request when using gwt-upload and for decoding the GWT-RPC request on the server-side for certain characters

Please find attached a few fixes to problems I had when using the portlet bridge with Tomcat + Liferay 6. These are:
- uploading files (via gwt-upload) required access to certain methods in the resource requests that weren't implemented according to the specification.
- encode/decode of GWT-RPC calls failed for certain data, e. g. '%' and '+' characters. The reason for this was that the request was decoded twice on the server side (the first time by the server, the second time by the bridge's `GwtServiceServletRequest` class.

I didn't test this against any other combination of servlet container / application server / portal.