Added an informative error check when passing in a refiner with an incompatible scheme to build PtexIndices.  Also fixed an assert to not check for an explicit scheme type, and use traits instead.
Added an informative error check when passing in a refiner with an incompatible scheme to build PtexIndices.  Also fixed an assert to not check for an explicit scheme type, and use traits instead.

lookup1980/OpenSubdiv,poljere/OpenSubdiv,takahito-tejima/OpenSubdiv,nyotis/OpenSubdiv,poljere/OpenSubdiv,nyotis/OpenSubdiv,xldeveloper/OpenSubdiv,anshuarya/OpenSubdiv,anshuarya/OpenSubdiv,c64kernal/OpenSubdiv,takahito-tejima/OpenSubdiv,shengfuintel/OpenSubdiv,xldeveloper/OpenSubdiv,c64kernal/OpenSubdiv,c64kernal/OpenSubdiv,xldeveloper/OpenSubdiv,lookup1980/OpenSubdiv,lookup1980/OpenSubdiv,shengfuintel/OpenSubdiv,anshuarya/OpenSubdiv,poljere/OpenSubdiv,nyotis/OpenSubdiv,shengfuintel/OpenSubdiv,takahito-tejima/OpenSubdiv