warn if headLink undefined, closes #343
warn if headLink undefined, closes #343

openhumanoids/director,manuelli/director,manuelli/director,mitdrc/director,openhumanoids/director,patmarion/director,mitdrc/director,manuelli/director,mitdrc/director,manuelli/director,patmarion/director,openhumanoids/director,patmarion/director,mitdrc/director,openhumanoids/director,patmarion/director,mitdrc/director,patmarion/director,manuelli/director,openhumanoids/director