- Added serialization to btBvhTriangleMeshShape/btOptimizedBvh. See ConcaveDemo for example usage.

- added bt32BitAxisSweep3, which co-exists without recompilation, using template class. This broadphase is recommended for large worlds with many objects (> 16384), until btMultiSwap is finished.
- Fixed some recent issues in Bullet 2.57 related to compound (thanks Proctoid) and memory allocations

src/LinearMath/btStackAlloc.h

@@ -55,6 +55,12 @@ public:
 		}
 		
 	}
+
+	int	getAvailableMemory() const
+	{
+		return totalsize - usedsize;
+	}
+
 	unsigned char*			allocate(unsigned int size)
 	{
 		const unsigned int	nus(usedsize+size);