Added new soldier flags: SOLDIER_BACK_ATTACK, SOLDIER_SNEAK_ATTACK (work for punch and stab attacks only).

ClosestKnownOpponent() now can return ID of closest opponent.
CalcCoverValue: improved code to avoid friendly fire.
EVENT_SoldierBeginPunchAttack: use supplied gridno as sTargetGridNo may not be set yet

Boxing:
- added possibility of counterattack after failed attack
- added possibility of opportunity attack a passing enemy
- bonus in CTH for boxers for attack from the back

Boxing AI:
- for boxers, always use high morale so that they attack
- cautious boxer approach, reserve AP for two attacks (only if not attacking from the back)
- try to avoid frontal attack
- sometimes boxer may decide to restore breath instead of moving and attacking
- boxer can step back to move away from opponent, if he is low on breath
- improved main boxer AI

git-svn-id: https://ja2svn.mooo.com/source/ja2/trunk/GameSource/ja2_v1.13/Build@8876 3b4a5df2-a311-0410-b5c6-a8a6f20db521

Tactical/Soldier Control.h

@@ -429,6 +429,8 @@ enum
 #define SOLDIER_DRAG_SOUND					0x00080000					// played sound when started dragging
 #define SOLDIER_SPENT_AP					0x00100000					// soldier has spent some AP this turn (including realtime)
 #define SOLDIER_TURNCOAT					0x00200000					// this enemy soldier will switch to the militia team if ordered to
+#define SOLDIER_BACK_ATTACK					0x00400000					// soldier was attacked from the back
+#define SOLDIER_SNEAK_ATTACK				0x00800000					// soldier was attacked by unseen enemy
 
 #define SOLDIER_INTERROGATE_ALL				0x000001F8					// all interrogation flags
 // ----------------------------------------------------------------