Use named constants instead of some magical constants in hgrunt code

dlls/hgrunt.cpp

@@ -278,7 +278,7 @@ void CHGrunt::GibMonster( void )
 	Vector vecGunPos;
 	Vector vecGunAngles;
 
-	if( GetBodygroup( 2 ) != 2 )
+	if( GetBodygroup( GUN_GROUP ) != GUN_NONE )
 	{
 		// throw a gun if the grunt has one
 		GetAttachment( 0, vecGunPos, vecGunAngles );
@@ -604,7 +604,7 @@ void CHGrunt::TraceAttack( entvars_t *pevAttacker, float flDamage, Vector vecDir
 	if( ptr->iHitgroup == 11 )
 	{
 		// make sure we're wearing one
-		if( GetBodygroup( 1 ) == HEAD_GRUNT && ( bitsDamageType & (DMG_BULLET | DMG_SLASH | DMG_BLAST | DMG_CLUB ) ) )
+		if( GetBodygroup( HEAD_GROUP ) == HEAD_GRUNT && ( bitsDamageType & (DMG_BULLET | DMG_SLASH | DMG_BLAST | DMG_CLUB ) ) )
 		{
 			// absorb damage
 			flDamage -= 20;