WIP Subsurf ptex coords

WIP tex image node

WIP GPU stuff

WIP add ptex vertex attrib to DerivedMesh for GPU drawing

WIP cycles packed texture stuff

WIP Ptex texture packing

WIP imbuf hacks

Silence warning in Ptex

Update CMakeLists for ptex

Temporary customdata mask tweak

Tweak texture-coord node to add Ptex UVs

WIP add Ptex UVs to Cycles mesh

Tesselation for Ptex loop layer

Import ptex-2.0.42 into extern/ptex

Temporary change to add-vcol operator to also add Ptex loop layer

RNA updates for Ptex

Move Cycles' Ptex attribute from vertices to corners

Add a couple new CustomData layers for Ptex

Add some Ptex types to Mesh SDNA

De-duplicate large block of shared code for GL vert attribs

Code in ccgdm_draw_attrib_vertex() was entirely the same as the top
portion of the code in cddm_draw_attrib_vertex(). Moved this code to a
new function, DM_draw_attrib_vertex().

ccgdm_draw_attrib_vertex() was removed in favor of calling
DM_draw_attrib_vertex(). cddm_draw_attrib_vertex() still does a couple
extra things, so it still exists but calls DM_draw_attrib_vertex().

In the interest of easy code review, no changes made to the code in
DM_draw_attrib_vertex() other than the new name and an added comment.

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D1010