Made all tests execute in the same VM, concurrently

* Changed from [offline instrumentation](http://www.eclemma.org/jacoco/trunk/doc/offline.html)
  to "online" instrumentation. With offline instrumentation it
  wasn't possible (Due to a "Class is already instrumented" error)
  to run several test runs without doing a clean in between.

* Fixed thread issue in LocalesTest that made it unreliable