Simplify a condition in refutes()

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Better annotate unlikely conditions

And in case of gcc we win also a small
speed optimization due to better branch
prediction.

No functional change.
Don't use __builtin_expect

Partially revert previous patch and use
unlikey() just as code annotation.

Actually it is better to rely on a profiler for branch prediction:

http://blog.man7.org/2012/10/how-much-do-builtinexpect-likely-and.html

"In fact, even when only one in ten thousand values is nonzero,
we're still at only roughly the break-even point"

No functional change,
Drop grep and tr dependency in Makefile

Use only sed to get the bench signature.

No functional change.
Sync with master

bench: 4558173
RookOn7th (+5, +10) + BishopPin (-10, 0)

bench: 4815099