Fix FarStencilFactory control stencil caching
Fix FarStencilFactory control stencil caching

The logic that invalidates the vertices in the control stencil and
the cached bspline patch weights was not triggering correctly.
Hopefully this new bit of logic should clear up some of the incorrect results.

fixes #246

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