Upgrade test project to Grails 2.4

I went ahead and upgraded the test project to Grails 2.4.  This pull request also includes the fix to MediaTypeParser that matches Grails-core DefaultAcceptHeaderParser. 

I upgraded the project by first creating a new project with grails create-app, then proceeded to copy all of the relevant files back into the project.  Since the test project was based on 2.2.1, many of the conf files have changed.  

Grails introduced forked mode recently which is incompatible with many of the functional tests as they are currently written.  I've disabled it here, but if you are interested, I can implement the fix to get them working with forked mode.

All the tests pass except for 1, "Test create nested resource as json" in RestfulApiControllerFunctionalSpec.  I'll work on getting this one to pass.