change version_set.cc table:  reduce size of level-3 to reduce write amplification in early compactions, raise size increment from 10x to 20x for levels 4, 5, and 6.
remove extra Finalized() calls used with previous threading model.  Only allow aggressive delete on non-overlapping levels.
correct loop exit condition as spotted in code review
Merge pull request #119 from basho/mv-tuning5

mv tuning5