Added 'xhr' as callback in JqueryEngineHelper::request() so it formats as Javascript.
Added test case for JqueryEngineHelper::request() to validate 'xhr' callback.
Removed /mpm from 'url' option for last test in JqueryEngineHelper::testRequest().
Merge pull request #2153 from Cameri/master

Added 'xhr' as callback in JqueryEngineHelper::request() so it formats as Javascript.