Blender Git Loki

== Ptex ==

initial ptex integration

* added the ptex C++ library to extern

* wrote a small C api for the library; just the functions I've used so
far are in the C api, but easy to add more

* added a new CustomData type (face data), stored as struct MPtex

* added RNA for CD_MPTEX

* each MPtex stores:
** the U- and V-resolution (always a power of two)
** the number of color channels (e.g. RGB or RGBA)
** the data type (can be bytes, shorts, or floats)
** the number of subfaces (for triangles now, will work also for ngons)

* for drawing ptex, one power of two texture is assigned to each face
** for quads, the texture is mapped normally across the full face
** for triangles, the face is split into four quads for drawing, and each
subface gets an equal-sized portion of the texture
** the texture is created with the same internal format as the ptex layer

* added an operator for loading ptex files

* added an operator for creating ptex layers; takes data type, number of
channels, and texel density as inputs. has some hackish code to allocate
texels based on a faces catmull-clark limit surface area

* added a simple ptex UI, shows ptex layers in the mesh data panel

* modified vpaint to paint on ptex instead of mcols


partial todo list:
* VBO drawing (make sure to turn VBO off before testing ptex for now)
* ptex saving
* better texel allocation
* upsampling/downsampling faces
* UI for setting individual faces' resolutions