Simplify aspiration window loop

Don't open the window in case we find a mate score: this
will be takes care with next patch.

No functional change.
Center aspiration window on last returned score

bench: 4428212
Merge branch 'master' into aspiration
Increase earlier aspiration window size

bench: 4377851
Revert "Increase earlier aspiration window size"

This reverts commit b88bc7b7667fc6ddbfc7412fb2c0bfc13e3bf11c.
Merge branch 'master' into aspiration

bench: 4507288
Disable flto when debugging

Link-time optimization does not work well with
generation of debugging information:

http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

Reported by Louis Zulli

No functional change.
Simplify aspiration window code

Here the main difference is that now we center
aspiration window on last returned score. This allows
to simplify handling of mate scores.

We have done a reversed SPRT tests, where we wanted to
verify if master is stronger than this patch.

Long TC: master vs this patch (reverse test)
LLR: -2.95 (-2.94,2.94)
Total: 37992 W: 7012 L: 6920 D: 24060

bench: 4507288
Workaround github issue

Temporary revert aspiration window patch
so to be visible to everybody: it will be
re-applied with next patch

No functional change (together with next one)
Simplify aspiration window code

Here the main difference is that now we center
aspiration window on last returned score. This allows
to simplify handling of mate scores.

We have done a reversed SPRT tests, where we wanted to
verify if master is stronger than this patch.

Long TC: master vs this patch (reverse test)
LLR: -2.95 (-2.94,2.94)
Total: 37992 W: 7012 L: 6920 D: 24060

bench: 4507288
Skip node-level cut-off tests when in check

No functional change.
Simplify "fail high upon reduction" in null search

Do not use threat move to detect the condition. This
let us to retire the big allows() function.

Test at short TC was within 50% score:
LLR: -2.95 (-2.94,2.94)
Total: 38272 W: 7941 L: 7940 D: 22391

To be verified with reverse long TC

bench: 4191565
Revert previous patch

Unfortunatly a reverse test at long TC failed:

master^ vs master
LLR: 1.37 (-2.94,2.94)
Total: 33682 W: 6294 L: 6071 D: 21317

So becuase short TC score is 50% there is a good
possibility patch is not scalable.

So revert it.

bench: 4507288
Don't IID when in check also in PvNodes

This tiny functional change allows to
nicely simplify things.

Performed at 50% in short TC:
LLR: -0.43 (-2.94,2.94)
Total: 46406 W: 9681 L: 9565 D: 27160

And succesfully passed long TC reverse test:
LLR: -2.95 (-2.94,2.94)
Total: 4945 W: 858 L: 937 D: 3150

bench: 4507230
Fix a crash with depth 1 perft

Bug recently introduced in e215a88cddd16e09

No functional change.