use size_t instead of int, for allocator

added hashtable based PairManager, thanks Pierre Terdiman and Erin Catto
improved friction in 'cachefriendly' solver
moved 'refreshcontactpoints' into collision detection, instead of solver
avoid linear search for contact manifolds, by storing an index
ignore margin for sphere shape (its entire radius is already margin)
avoid alignment checks in BVH serialization, they don't compile on 64-bit architectures
made 'bomb' box more heavy

src/LinearMath/btScalar.h

@@ -288,6 +288,13 @@ SIMD_FORCE_INLINE float btSelect(unsigned condition, float valueIfConditionNonZe
 #endif
 }
 
+template<typename T> inline void btSwap(T& a, T& b)
+{
+	T tmp = a;
+	a = b;
+	b = tmp;
+}
+
 
 //PCK: endian swapping functions
 SIMD_FORCE_INLINE unsigned btSwapEndian(unsigned val)