fix in structure alignment of btMultiBodyLinkDoubleData and btMultiBodyDoubleData

causing serialization issue in  URDF/SDF loading in double-precision mode on Windows 32bit.
(it was fine on Mac/Linux 64bit)
bump serialization version to 2.85, as we change the file format
fix in name clash in makesdna.cpp -> intptr_t is already defined.

examples/Importers/ImportURDFDemo/ImportURDFSetup.cpp

@@ -1,7 +1,7 @@
 
 #include "ImportURDFSetup.h"
 #include "BulletDynamics/ConstraintSolver/btGeneric6DofSpring2Constraint.h"
-
+//#define TEST_MULTIBODY_SERIALIZATION 1
 
 #include "BulletDynamics/Featherstone/btMultiBodyLinkCollider.h"
 #include "Bullet3Common/b3FileUtils.h"
@@ -377,6 +377,7 @@ void ImportUrdfSetup::initPhysics()
 		
 	}
 
+
 #ifdef TEST_MULTIBODY_SERIALIZATION
 	m_dynamicsWorld->serialize(s);
 	b3ResourcePath p;