Check OpenCL version before calling enqueue_fill_buffer()

This adds a check for OpenCL version 1.2 before calling the
enqueue_fill_buffer() function in the fill() algorithm.
Skip tests requiring OpenCL 1.2 on usupported devices
Merge pull request #189 from ddemidov/skip-1.2-tests

Skip tests requiring OpenCL 1.2 on devices that do not support OpenCL 1.2