Improve compatibility with older versions of Mac OS X

Use the -mmacosx-version-min flag to support older versions of Mac OS X
(like version 10.6 and 10.7) when compiled on a machine running version
10.8.
Sync qsearch with search

Port to qsearch() the same changes we recently
added to search().

Overall this search refactoring series shows
almost 2% speed up on gcc compile.

No functional change.
Add Contempt Factor in Polyglot

The contempt factor was previously not included in polyglot.ini
Merge pull request #29 from RyanTaker/patch-3

Add Contempt Factor to Polyglot.ini
Rearrange prefetch code

No functional change.
Retire is_dangerous() and inline its content

No functional change.
Introduce arm-32 ARCH in Makefile

No functional change.
ARM lsb/msb assembly

Implement lsb/msb using armv7 assembly instructions.
msb is the easiest one, using a gcc intrinsic that generates
code using the ARM's clz instruction. lsb is also using this
clz instruction, but with the help of ARM's 'rbit' (bit
reversing) instruction. This leads to a >2% speed gain.

I also renamed 'arm-32' to the more meaningfull 'armv7' in the Makefile

No functional change.
Fix a minor bug in search

As Joona says: "The problem is that when doing full
window search (-VALUE_INFINITE, VALUE_INFINITE), and
pruning all the moves will return fail low which is
mate score, because only clause touching alpha is
"mate distance pruning". So we are returning mate score
although we are just pruning all the moves. In reality
there probably is no mate in sight.

Bug spotted and fixed by Joona.
Scale contempt factor to zero at endgame

Contempt Factor is more effective at opening/middle game
and seems harmful at endgame phase. See:

http://chessprogramming.wikispaces.com/Contempt+Factor

http://web.archive.org/web/20070707023203/www.brucemo.com/compchess/programming/contempt.htm

Therefore we scale down the contempt factor while going
on with the game so to reach zero at endgame phase.

No functional change.
Retire can_return_tt() and rewirte TT-hit code

Simplify the code and doing this introduce a couple
of (very small) functional changes:

- Always compare to depth even in "mate value" condition
- TT cut-off in qsearch also in case of PvNode, as in search

Verified against regression with 2500 games at 30"+0.05
on 2 threads: 451 - 444 - 1602

Functional changed: new bench is 5544977
Use new 64 bit De Bruijn BitScan

Allows to sync 32 and 64 bits implementations.

Idea by Kim Walisch, reported by Gerd Isenberg:
http://talkchess.com/forum/viewtopic.php?t=45554

No functional change.
Retire BitCount8Bit[] table

Use popcount() instead in the only calling place.
It is used only at initialization so there is no
speed regression and anyhow even initialization
itself is not slowed down: magic bitboard setup
stays around 175 msec on my slow 32bit Core Duo.

No functional change.
Move all Contempt Factor code to search.cpp

Where it is used.

No functional change.
Set TT size to 32 MB during 'bench'

On some platforms 128 MB of RAM for TT is too much,
so run 'bench' with the default 32 MB size.

No functional change although of course now 'bench'
reports a different number: 5545018
Document why is safe ttValue == VALUE_NONE

We can have ttValue == VALUE_NONE when we use a TT
slot to just save a position static evaluation, but
in this case we also save DEPTH_NONE so to avoid
using the ttValue in search. This happens to work,
but due to a number of lucky and tricky cases that
we now documnet through a bunch of asserts and a
little change to value_from_tt() that has no real
effect but clarifing the code.

No functional change.
Fix Makefile for PowerPC with prefetch enabled

Existing Makefile is buggy for PowerPC, it has no
SSE, yet it is given it if Prefetch is enabled,
because it isn't ARMv7.

Patch from Matthew Brades.

No functional change.
Further improve compatibility when compiling on OS X

Change the minimum supported version from 10.6 to 10.0
Merge pull request #33 from daylen/master

Further improve OS X compatibility

Change the minimum supported version from 10.6 to 10.0

No functional change.

Fix compatibility with old Windows 95 and 98

Report and patches by bnemias.

No functional change.

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