First attempt at quiescent search.  Causes strange search explosions; don't use.

Causes generally bad behavior.  Need to figure out why before importing
into the main tree.
MVV/LVA, search termination

Added MVV/LVA evaluation to pawns.
Early termination of search.
Correctly terminate an aborted search.
Quiescence is still sort of bunk.
Merge branch 'quiescent-search'
Remove quiescent search entirely for now.  Renaming for clarity.