refactors context properties parsing and setting

- correctly calculate the length of the storage array.
- ensure that in a given key,value pair value is sensible. Necessary because properties has an odd length.
- rework control flow.
- context properties should not start with a zero.
adds test for context properties
Merge pull request #33 from JuliaGPU/vc/fixglctx

Context Properties parsing and setting
adds error codes from extensions and future OpenCL versions.
Merge pull request #36 from JuliaGPU/vc/error_codes

adds error codes from extensions and future OpenCL versions.
simplifies runtest and hopefully fixes travis
Merge pull request #38 from JuliaGPU/vc/travis

simplifies runtest and hopefully fixes travis
adds the functions necessary for interop between OpenCL and OpenGL
adds OCL11 opengl functions
adds missing constant
fixup: API for clGetGLContextInfoKHR
fix small errors
adds CreateFromGLTexture for OCL1.2
Merge branch 'opengl' into vc/qjulia

Conflicts:
	src/api.jl
	src/context.jl
	src/error.jl