Prismatic joint to rail joint

@Simeon or @John please take a look at this for a possibility in a future update:
http://box2d.org/forum/viewtopic.php?f=3&t=8297
It takes the prismatic joint and creates a guided rail (defined by splines or sine function it seems), this could be VERY useful for games. Thanks.

Video if you or others are interest (it’s in the link anyway):
https://www.youtube.com/watch?v=hTCIRk9vcGA

Also this implementation of a slider joint (Prismatic with min value and max value):
http://subversion.assembla.com/svn/C3RPGSysTest/GameSystemXNA_test_R2/Farseer%20Physics%20Engine%203.0%20XNA/Dynamics/Joints/SliderJoint.cs

I’m thinking this is one of the reasons Codea should open source the runtime…