Patch Set 5: Looks good to me, but someone else must approve; IP review completed

OK, I think this implementation is sane.  Its bloody fast:

 testDefault     Myers                 492139 ns    8 edits
 testDefault     Histogram             186391 ns    8 edits
 
 testIgnoreAll   Myers                1319354 ns    8 edits
 testIgnoreAll   Histogram             316697 ns    8 edits