This also removes the powermock dependency. Although powermock is a
fine library, it currently prevents dropping Junit4. And since we only
use the Whitebox API of powermock, this simply replaced powermock's
Whitebox with our own.
It appears that we observe a partion GC run on some systems,
especially ones with few resources. Hopefully this increases the
chances to observe the expected GC affects so that the unit test
passes also on those systems.
Because an failing test on Travis was observered using a timeout of
60s:
org.jivesoftware.smackx.muc.MucMemoryLeakTest > mucMemoryLeakTest FAILED
java.lang.AssertionError: No reference found after 60000ms
at org.junit.Assert.fail(Assert.java:88)
at org.junit.Assert.assertTrue(Assert.java:41)
at org.junit.Assert.assertNotNull(Assert.java:712)
at org.jivesoftware.smack.util.MemoryLeakTestUtil.assertReferencesQueueSize(MemoryLeakTestUtil.java:110)
at org.jivesoftware.smack.util.MemoryLeakTestUtil.noResourceLeakTest(MemoryLeakTestUtil.java:103)
at org.jivesoftware.smackx.muc.MucMemoryLeakTest.mucMemoryLeakTest(MucMemoryLeakTest.java:29)