proper/correct synchronization on hashmap to avoid ConcurrentModificationException
Merge remote-tracking branch 'tbsandee/robolectric-2-concurrentmodexception'

* tbsandee/robolectric-2-concurrentmodexception:
  proper/correct synchronization on hashmap to avoid ConcurrentModificationException

Conflicts:
	src/main/java/org/robolectric/bytecode/ClassCache.java