Draw contexts do not fully initialize patch arrays #281

* added the numVertexElements argument to Osd*DrawContext::Create, which is used to initialize the patch arrays when calling OsdDrawContext::ConvertPatchArrays
* removed the unused level argument from Osd*DrawContext::_initialize
* maintenance work on CL/D3D11 bindings to get them to compile
Changed FindGLFW.cmake so that setting the %GLFW_LOCATION% environment variable in Windows behaves like the CMake option, "-DGLFW_LOCATION=%GLFW_LOCATION%".
Fix a bug of OsdUtilMeshBatch, the varying buffer isn't computed with CL kernel.
Merge pull request #282 from nathan-at-digitalfish/issue281

Draw contexts do not fully initialize patch arrays #281
Merge pull request #283 from nathan-at-digitalfish/fix_find_glfw

Change to FindGLFW.cmake for Windows