Revert "Check for an available slave early on"

This reverts commit ce1c260ea97c14eea

It seems we haev an important nps drop
in endgames with high threads.

Reported by fastgm, testing with 16 threads.

bench: 7710548
Pack 3 TT entries in 32 bytes cluster

This patch compresses TTEntry to 10 bytes
and resizes a cluster from 4 to 3 slots, so
that cluster size is 10 X 3 + 2 = 32 bytes
where last 2 bytes are padding.

Patch gives and advantage under high hash
pressure where we can reach +10 ELO with
4 MB Hash at 60secs TC:

ELO: 10.24 +-2.0 (95%) LOS: 100.0%
Total: 40000 W: 7830 L: 6651 D: 25519

And is neutral with low hash pressure.

To note that now hash key size is just 16bits
opening the door for many more hash collisions,
eventually big number of tests under many different
conditions seem to confirm that this is not so
dangerous as it seems.

Idea from Ron Britvich

Code reworked by Marco Costalba and Joona Kiiski

Tested with high hash perssure.

Passed STC (16MB hash size)
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 14066 W: 2445 L: 2308 D: 9313

and LTC (8MB hash size)
LLR: 2.96 (-2.94,2.94) [0.00,6.00]
Total: 8827 W: 1297 L: 1161 D: 6369

Tested also for no regression at 128MB hash size:
LLR: 2.94 (-2.94,2.94) [-3.50,0.50]
Total: 18451 W: 3286 L: 3177 D: 11988

Bench: 8095369
Increase max hash size to 64GB

Now that TT cluster ize is 32bytes and
we address TT table by cluster, it is
possible to raise the limit to 64GB
while still using a uint32_t to index
the cluster within teh table.

No functional change.
Fix an assert in search

After recent patch 55a3e0af8d0d1e169c, we have
an assert searching on:

5rk1/4K1pp/8/5PPP/8/8/8/1R6 w - - 12 1

Assert is:

Assertion `-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE' failed.

The patch fixes it.

bench: 8094100