Extra thinking before accepting draw PVs.

Extra thinking before accepting draw PVs.

If the PV leads to a draw (3-fold / 50-moves) position
and we're ahead of time, think a little longer, possibly
finding a better way.

As this is most likely effective at higher draw rates,
tried speculative LTC after a yellow STC:

STC:
http://tests.stockfishchess.org/tests/view/59eb173a0ebc590ccbb8975d
LLR: -2.95 (-2.94,2.94) [0.00,5.00]
Total: 56095 W: 10013 L: 9902 D: 36180
elo =    0.688 +-    1.711 LOS:   78.425%

LTC:
http://tests.stockfishchess.org/tests/view/59eba1670ebc590ccbb897b4
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 59579 W: 7577 L: 7273 D: 44729
elo =    1.773 +-    1.391 LOS:   99.381%

bench: 5234652