[ODE] bug in dxHeightfieldData dtor

[David Walters]

> There's a small bug in the dxHeightfieldData() destructor. It attempts to free the sample data by
> deleting a void pointer. AFAIK it needs to be typecast to the correct type, otherwise the behavior
> is undefined (although it compiles/runs fine on VC++2005), correct?

Ah, okay -  I thought my fix to cast from a const void* to a void*
would have fixed it - assuming the warning was due to the const nature
of the pointer, it seems that I was wrong. You're right, it works fine
on Visual Studio 2003 too.

I'll put together a patch that fixes this at some point, I hope it's
still 'just' a warning and that you can carry on working with it...
never the less, it requires fixing.

Regards,
Dave.