make Bullet URDF parser more similar to the ROS URDF parser. There is still a difference in ordering of links,

due to the use of different hash-map implementations, with a difference in iterator order
(btHashMap versus std::hashmap)

examples/Importers/ImportURDFDemo/URDFImporterInterface.h

@@ -15,6 +15,10 @@ public:
 	virtual ~URDFImporterInterface() {}
 	
  
+    virtual bool loadURDF(const char* fileName)=0;
+
+    virtual const char* getPathPrefix()=0;
+    
     ///return >=0 for the root link index, -1 if there is no root link
     virtual int getRootLinkIndex() const = 0;