Fix edge-only face-varying interpolation.
Fix edge-only face-varying interpolation.

For face-varying interpolation, sharpness should be interpreted as an
infintely sharp boundary. Hbr implements this correctly for vertex
sharpness, but inconsistently for edge sharpness: both the fvarbits
cache and methods that gather face-varying sharpness need to be corrected.

fixes #231

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