Add API to get user constraint id.

examples/pybullet/examples/constraint.py

@@ -9,6 +9,8 @@ cubeId = p.loadURDF("cube_small.urdf",0,0,1)
 p.setGravity(0,0,-10)
 p.setRealTimeSimulation(1)
 cid = p.createConstraint(cubeId,-1,-1,-1,p.JOINT_FIXED,[0,0,0],[0,0,0],[0,0,1])
+print cid
+print p.getConstraintUniqueId(0)
 prev=[0,0,1]
 a=-math.pi
 while 1:
@@ -21,4 +23,4 @@ while 1:
 	orn = p.getQuaternionFromEuler([a,0,0])
 	p.changeConstraint(cid,pivot,jointChildFrameOrientation=orn, maxForce=50)
 
-p.removeConstraint(cid)
+p.removeConstraint(cid)