mcostalba/Stockfish — pull request #157 by stsu (2014-01-11 16:34:39+00:00)
Title: Enhanced exchnage rules, pawn wideness, rammed pawns and enhanced draw detection

All the changed combined in this repository (after fork) gives my test result +49 ELO.

Seems most important is the exchange rule : When ahead at least a piece, exchange pieces not pawns.
and to some degree the draw detection : Low pawn->wideness check for draw.