Slight tweak to king safety.  Bench: 5534531
Merge Gary's king safety tweak

Still well within error bars, so probably not a big improvement,
but may be worthwhile. I will let the test keep running. The idea
for the tweak came from the TCEC game against Houdini. Stockfish saw
it as a draw, well past when it should have seen problems. King safety
was off, since it was QN and pawns only, but in fact the king was
quite vulnerable.

After 8000 games at 60/1 (Gary's test)

ELO: -0.43 +- 99%: 10.02 95%: 7.62
Wins: 1235 Losses: 1245 Draws: 5520 Total: 8000

PGN of game against houdini. Moves 55-59 it was seeing a draw, and
Houdini was seeing a good sized advantage for black. With the change,
Stockfish now recognizes that moving the king there is a bad idea.

[Event "nTCEC - Stage 1 - Season 1"]
[Site "http://www.tcec-chess.net"]
[Date "2013.02.07"]
[Round "4.2"]
[White "Stockfish 2.31"]
[Black "Houdini 3.0"]
[Result "0-1"]
[Variant "normal"]

1. Nf3 Nf6 2. c4 e6 3. Nc3 Bb4 4. Qc2 O-O 5. a3 Bxc3 6. Qxc3 b6 7. b4 a5 8. Bb2
axb4 9. axb4 Rxa1+ 10. Bxa1 Na6 11. e3 Qe7 12. b5 Nc5 13. Qc2 Bb7 14. Be2 d6
15. O-O Ra8 16. Bb2 h6 17. Ra1 Rxa1+ 18. Bxa1 e5 19. Qa2 Be4 20. Ne1 Bg6
21. Bb2 Kh7 22. f3 Nfd7 23. Bc3 h5 24. Qa1 h4 25. Kf1 Qf6 26. Qa7 Qd8 27. Qa2
e4 28. Qa1 h3 29. g3 exf3 30. Nxf3 Bf5 31. Bd4 g6 32. Kf2 Kg8 33. Qa3 Bg4
34. d3 Qc8 35. Bxc5 bxc5 36. Ke1 Qb7 37. e4 Bxf3 38. Bxf3 Ne5 39. Be2 Qc8
40. Qa6 Qd8 41. Qa5 Kh7 42. Kd1 Kg7 43. Qa7 Kg8 44. Qa5 Kh7 45. Qa7 Kg7 46. Qa5
Qb8 47. Kd2 Kh7 48. Kc2 Kg8 49. Qa6 Qd8 50. Qa5 Qf6 51. Qe1 Kg7 52. Qf1 Qe6
53. Qe1 Qd7 54. Qc1 Qe8 55. Kc3 Qa8 56. Kb3 Kh7 57. Qa3 Qd8 58. Qc1 c6 59. Qc3
Qb6 60. Ka4 Qb7 61. Qd2 Nd7 62. Qc3 Qa7+ 63. Kb3 Kg8 64. Bg4 cxb5 65. cxb5 Nb6
66. Bxh3 Qa4+ 67. Kb2 Qd1 68. Ka3 Qe2 69. Kb3 Qh5 70. Bg2 Qxh2 71. Qf6 Qxg3
72. Bf1 Qe3 73. Kc2 Na4 74. b6 Nxb6 75. Qd8+ Kg7 76. Qxb6 Qf2+ 77. Kc3 Qxf1
78. Qxd6 Qf6+ 79. Qxf6+ Kxf6 80. Kc4 g5 81. Kxc5 Ke5 82. d4+ Kxe4 83. d5 g4
84. d6 g3 85. d7 g2 86. d8=Q g1=Q+ 87. Kb5 Qb1+ 88. Ka4 Qa2+ 89. Kb4 f5
90. Qe8+ Kf4 91. Qg6 Qd5 92. Qg1 Qe4+ 93. Ka5 Qe2 94. Qg8 Kf3 95. Qd5+ Qe4
96. Qd1+ Kg2 97. Qd2+ Kf1 98. Qh2 f4 99. Qh3+ Ke2 100. Qg4+ Kd2 101. Qg5 Kc2
102. Qh4 0-1

bench: 5518286
Account for gamePly after each move

Rename startPosPly to gamePly and increment/decrement
the variable after each do/undo move. This adds a little
overhead in do_move() but we will need to have the
game ply during the search for the next patches now
under test.

Currently we don't increment gamePly in do_null_move()
becuase it is not needed at the moment. Could change
in the future.

As a nice side effect we can now remove an hack in
startpos_ply_counter().

No functional change.
Merge remote-tracking branch 'upstream/master'