OpenImageIO: add version 1.3.12
blender: remove scm

They switched to git an I am too lazy to test it after fixing
SCM_REPOSITORY.
blender: bump to version 2.70

 * use python.exlib's api 2 to require a specific python version
 * remove the options bullet, elbeem, gameengine and player because they
   don't add any dependencies
 * add a libav option
 * hard enable OpenImageIO because they are required for the cycles
   renderer
 * hard enable tiff and openexr because we already indirectly depend on
   it through OpenImageIO
 * enable the cycles renderer
 * remove cmake options that are identical to the default
 * use cmake api 2
 * fail if openmp is enabled but not supported