Work on cleaning up EntityDiff

Patchset 12: Patching operated on a copy, changed
	to operation of the original.
Patchset 13: Switched a test that previously had
	its then- and elseclauses switched.
Patchset 14: Changed base to current during patching,
	added an additional testcase for a change of
	diff op.

Change-Id: I877d690f3872fdee7c7946a646faf25e47c2ccd7