Add flags to btRigidBody to disable world gravity.

Use setFlags/getFlags with BT_DISABLE_WORLD_GRAVITY

See http://code.google.com/p/bullet/issues/detail?id=324

src/BulletDynamics/Dynamics/btRigidBody.h

@@ -38,6 +38,10 @@ extern bool gDisableDeactivation;
 #endif //BT_USE_DOUBLE_PRECISION
 
 
+enum	btRigidBodyFlags
+{
+	BT_DISABLE_WORLD_GRAVITY = 1
+};
 
 
 ///The btRigidBody is the main class for rigid body objects. It is derived from btCollisionObject, so it keeps a pointer to a btCollisionShape.
@@ -83,6 +87,10 @@ class btRigidBody  : public btCollisionObject
 	//keep track of typed constraints referencing this rigid body
 	btAlignedObjectArray<btTypedConstraint*> m_constraintRefs;
 
+	int				m_rigidbodyFlags;
+	
+	int				m_debugBodyId;
+
 public:
 
 	///The btRigidBodyConstructionInfo structure provides information to create a rigid body. Setting mass to zero creates a fixed (non-dynamic) rigid body.
@@ -503,7 +511,15 @@ public:
 		return m_constraintRefs.size();
 	}
 
-	int	m_debugBodyId;
+	void	setFlags(int flags)
+	{
+		m_rigidbodyFlags = flags;
+	}
+
+	int getFlags() const
+	{
+		return m_rigidbodyFlags;
+	}
 
 	virtual	int	calculateSerializeBufferSize()	const;