Cleaner code to go through the watches
Allowing no-stats-check for implicit subsumer
Doing implicit subsumption before BVA -- it would interfere anyway

Not only with the heuristics but also with the actual algorithm.
Although it is taken care of in any case, it's better to clean before
anyway, so that internal cleaner algorithm doesn't have to bother much
A much cleaner sorter algorithm for implicit subsumption