Dynamic aspiration search without research.

Implement system where aspiration search window is calculated using
values from previous iterations.

And then some crazy experimental stuff: If search fails low at the root,
don't widen window, but continue and hope we will find a better move
with given window. If search fails high at the root, cut immediately,
add some more time and start new iteration.

Note: this patch is not complete implementation, but a first test
for this idea. There are many FIXMEs left around. Most importantly
how to deal with the situation when we don't have any move!

Signed-off-by: Marco Costalba <mcostalba@gmail.com>