Log Message:
Import ptex-2.1.28 as graphics/ptex.

Ptex is a texture mapping system developed by Walt Disney Animation Studios for
production-quality rendering:

 - No UV assignment is required! Ptex applies a separate texture to each face
   of a subdivision or polygon mesh.

 - The Ptex file format can efficiently store hundreds of thousands of texture
   images in a single file.

 - The Ptex API provides cached file I/O and high-quality filtering, everything
   that is needed to easily add Ptex support to a production-quality renderer
   or texture authoring application.