Use Box2D's callbacks for destruction of physics objects and wait until the end of the timestep before destroying them.

Merge of box2d-id2 from love-experiments

src/modules/physics/box2d/Joint.h

@@ -78,6 +78,12 @@ namespace box2d
 
 		virtual ~Joint();
 
+		/**
+		* Returns true if the joint is active in a Box2D world.
+		**/
+		bool isValid() const;
+
+
 		/**
 		* Gets the type of joint.
 		**/
@@ -103,25 +109,27 @@ namespace box2d
 
 		bool getCollideConnected() const;
 
-	protected:
-
 		/**
 		* Joints require pointers to a Box2D joint objects at
 		* different polymorphic levels, which is why these function
 		* were created.
 		**/
 
+		/**
+		* Destroys the joint. This function was created just to
+		* get some cinsistency.
+		**/
+		void destroyJoint(bool implicit = false);
+
+	protected:
+
 		/**
 		* Creates a Joint, and ensures that the parent class
 		* gets a copy of the pointer.
 		**/
 		b2Joint * createJoint(b2JointDef * def);
 
-		/**
-		* Destroys the joint. This function was created just to
-		* get some cinsistency.
-		**/
-		void destroyJoint(b2Joint * joint);
+
 	};
 
 } // box2d