Fix btSoftBody issue, so it can interact with btCollisionObject and btGhostObject (and not just btRigidBody and btSoftBody)

Thank for the report mi076 http://www.bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=9&t=2823

remove legacy.c from libxml
removed #include <math.h> from btQuadWord.h , it should be centralized in btScalar.h (to allow easier replacement with fastmath.h etc)

src/BulletSoftBody/btSoftBody.cpp

@@ -2600,7 +2600,7 @@ void			btSoftBody::defaultCollisionHandler(btCollisionObject* pco)
 	case	fCollision::CL_RS:
 		{
 			btSoftColliders::CollideCL_RS	collider;
-			collider.Process(this,btRigidBody::upcast(pco));
+			collider.Process(this,pco);
 		}
 		break;
 	}