Minor constraint refactoring, to allow SPU-side processing for PLAYSTATION 3 (added non-virtual methods)

Also comment-out some code for __SPU__ to reduce code size
Added btContactConstraint (only used on PS3 SPU right now, better to use btPersistentManifold directly for contact constraints)
Improved readblend utility library (see also usage in http://gamekit.googlecode.com with Irrlicht)

Fix for btConvexConvexAlgorithm, potential division by zero
Thanks linzner http://code.google.com/p/bullet/issues/detail?id=260

src/BulletMultiThreaded/SequentialThreadSupport.h

@@ -81,6 +81,11 @@ public:
 
 	virtual void setNumTasks(int numTasks);
 
+	virtual int getNumTasks() const
+	{
+		return 1;
+	}
+
 };
 
 #endif //SEQUENTIAL_THREAD_SUPPORT_H