refactor CL/CUDA specific initialization stuffs into
examples/common/clDeviceContext and cudaDeviceContext, and
update examples to use those structs.
also
- remove CL/CUDA tests from osd_regression. The tests for those kernels will be covered by glImaging.
- update cuda initialization to use the GL-interoperable device if available.
- remove CL specialization from glShareTopology, following the same pattern as we took in the previous OsdGLMesh refactoring. (still something strange with XFB kernels though)
- fix file permissions.
