[ODE] added dJointSetFeedback() and dJointGetFeedback()

[Russ Smith]

i've added dJointSetFeedback() and dJointGetFeedback(). if you don't
like the API for whatever reason, speak up now and it might get changed.

erwin, your core code for computing the feedback info is basically
unchanged, thanks for this. your LCP problems i think should probably be
solved a different way than having a joint callback return value though
... or at least i want to understand how your solution can work ... can
you provide an example where your technique corrects the LCP problems?

the documentation for these functions is at:
  http://q12.org/ode/ode-latest-userguide.html
...as usual, along with a bit of discussion on the API decisions.

now i'm off to see some volcanos, be back in a week.

russ.

-- 
Russell Smith
http://www.q12.org