GREML: fix problem with parameter map for derivatives.
GREML: fix problem with parameter map for derivatives.

Joshua suggested this patch.

jpritikin/OpenMx,jpritikin/OpenMx,JuKa87/OpenMx,mhunter1/OpenMx,mhunter1/OpenMx,jpritikin/OpenMx,mhunter1/OpenMx,mhunter1/OpenMx,jpritikin/OpenMx,JuKa87/OpenMx,jpritikin/OpenMx,mhunter1/OpenMx,jpritikin/OpenMx,JuKa87/OpenMx,JuKa87/OpenMx,JuKa87/OpenMx,JuKa87/OpenMx,mhunter1/OpenMx