Rotate texture values when filtering for tangent-space textures

If the values stored in Ptex are vectors defined in tangent space of the face (from the ordered verticies; i.e using 0-1 and 0-3 as basis vectors), then filtering across edges does not work, as values across edges may be in a different space.

This modification allows a user to specify an EdgeFilterMode in a Ptex file to specify if the values are defined in this space or not. If they are, then the values are rotated during sampling, utilizing the UV sampling rotation to determine orientation.

This modification is only for PtexSeparableFilter, and PtexTriangleFilter is left untouched.