[ODE] Breakable joints

[Roel van Dijk]

> I'm almost done (I think). But I'm having a problem that I can't figure
> out. I need to detach a joint in step.cpp. But dJointAttach is not yet
> declared in step.cpp. I tried to make it visible by including
> <ode/objects.h>. But when I call dJointAttach I get this error message:
> 'ODE INTERNAL ERROR: unattached or disabled joint tagged'.
> Is it possible to detach joints in step.cpp? I want to detach it right
> after the 'compute constraint force' part of the dInternalStepIsland_x2
> function. That is where the constraint forces are calculated and I thought
> that it was the right place to check where a joint should be broken or not.
Solved. Now I just flag the joints that are broken. I detach them in in 
processIslands.