MOESI_hammer: cache flush support: Fix the deadlock issue, and clean up the changed files

In this version, I have redesigned the cache flushing mechanism for the case that 
the line is already in exclusive state in the cache. I think this implementation solves the 
reported deadlock issue.

I have also applied Brad's comments.

This implementation passes 1,000,000 ruby test cases, and is under test for 10,000,000 cases (with random_seed activated).