added test to assert that transaction push does not block other transactions
Merge pull request #1854 from lassewesth/commitpushcontention

added test to assert that transaction push does not block other transactions
Removes debug code left around
Fixes and enables test for unregistering Monitor listeners

The test MonitorsTest.shouldUnregister() was failing with a ClassCastException.
 The reason was that it was doing the cast on a field different than the one that
 it was performing the instanceof check. This error is now fixed and the test
 passes.