add btAlignPointer template and use it in serializer/allocator

this should fix Issue 559

src/LinearMath/btScalar.h

@@ -519,4 +519,21 @@ struct btTypedObject
 		return m_objectType;
 	}
 };
+
+
+///align a pointer to the provided alignment, upwards
+template <typename T>T* btAlignPointer(T* unalignedPtr, size_t alignment)
+{
+        union
+        {
+                T* ptr;
+                size_t integer;
+        };
+        const size_t bit_mask = ~(alignment - 1);
+        ptr = unalignedPtr;
+		integer += alignment-1;
+        integer &= bit_mask;
+        return ptr;
+}
+
 #endif //BT_SCALAR_H