pass wait_for to enqueue_fill_buffer backend
skip tests unsupported by pocl
test enqueue_barrier/marker and wait_for_events
test unload_platform_compiler
Merge pull request #52 from yuyichao/master

Add some tests for wrapper backend and skip some tests that are not supported by pocl.
Merge branch 'master' into cffi

Conflicts:
	test/test_wrapper.py
Minor PEP8 cleanup
Merge branch 'master' into cffi