Add get context platf. OCL ver. + Update queue creation to OCL 2.0

- Adjust code for new ccl_context_get_opencl_version(), namely in:
  * event_wrapper.c (event markers, barriers)
  * test_cad_programs.c
- OCL 2.0 uses new queue creation function, cf4ocl may optionally
use it if present in platform.
- Replace some @protected tags with @private