Add btGearConstraint, with a demo in Bullet/Demos/ConstraintDemo

Thanks to Dimitris Papavasiliou for the idea.

Demos/ConstraintDemo/main.cpp

@@ -1,18 +1,18 @@
 #include "ConstraintDemo.h"
 #include "GlutStuff.h"
 #include "GLDebugDrawer.h"
+
 #include "btBulletDynamicsCommon.h"
 
 int main(int argc,char** argv)
 {
 
-	GLDebugDrawer	gDebugDrawer;
+	
 
     ConstraintDemo* constraintDemo = new ConstraintDemo();
 	
 
     constraintDemo->initPhysics();
-	constraintDemo->getDynamicsWorld()->setDebugDrawer(&gDebugDrawer);
 	constraintDemo->setDebugMode(btIDebugDraw::DBG_DrawConstraints+btIDebugDraw::DBG_DrawConstraintLimits);
 	
 	return glutmain(argc, argv,640,480,"Constraint Demo. http://www.continuousphysics.com/Bullet/phpBB2/",constraintDemo);