Per Matt, allow build of examples without SimTK_INSTALL_DIR being set.
Per Matt, allow build of examples without SimTK_INSTALL_DIR being set.

elen4/simbody,elkingtonmcb/simbody,Gjacquenot/simbody,robojukie/simbody,simbody/simbody,Gjacquenot/simbody,elkingtonmcb/simbody,elen4/simbody,robojukie/simbody,scamille/simbody,chrisdembia/simbody,scamille/simbody,chrisdembia/simbody,elkingtonmcb/simbody,scamille/simbody,robojukie/simbody,chrisdembia/simbody,Gjacquenot/simbody,simbody/simbody