add enums for probe/release; again this is not properly parameterized and will only work on inner port of broadcast hub on MemtestConfig (MESICoherence policy)

I discovered is_builtin_type which needs to be considered when interpreting acquire/grant type field

 * SimpleHellaCacheIF now properly handles both the non-blocking data
   cache and blocking data cache.
 * SimpleHellaCacheIF maintains ordering of replayed requests
 * L2 VoluntaryReleaseTracker sends voluntary release grant properly
 * Coherence protocols now downgrade for probeCopy

Correct typo in heading