#5 fix GW linux build, windows link error

[Eric Sanford]

This patch is to fix add back Physics Drivers Newton,
TrueAxis, and Novodex. I do not know why they where
removed. Newton and TrueAxis work. If you have the evn
variables TrueAxisHome and/or NewtonHome defined build
will fail. Because configure adds the directory to the
variable PHYSICS_DRIVERS witch the
PhysicsDrivers/Makefile.am file adds to SUBDIR=, but
configure does not create the Makefiles. Novodex could
be removed, is it still available?

Second it adds definitions for functions that were in
the headers but not defined anywhere.
Joint::setUserData
Joint::getUserData
Parameter::isRequired

[Eric Sanford]

fix GW linux build, windows link error