Improve damping formula in btRigidBody::applyDamping

Thanks to sparkprime, see http://code.google.com/p/bullet/issues/detail?id=74
Fixed btCompoundShape/btCapsuleShape/btGImpactShape for missing m_shapeType, and added an assert in DemoApplication::localCreateRigidBody for invalid shape types.

src/BulletCollision/CollisionShapes/btCapsuleShape.cpp

@@ -21,6 +21,7 @@ subject to the following restrictions:
 
 btCapsuleShape::btCapsuleShape(btScalar radius, btScalar height) : btConvexInternalShape ()
 {
+	m_shapeType = CAPSULE_SHAPE_PROXYTYPE;
 	m_upAxis = 1;
 	m_implicitShapeDimensions.setValue(radius,0.5f*height,radius);
 }