Add argument validation for origin/region/pitch; disallow zero-sized regions
Workaround for an Intel CPU driver bug (user events with status -1 not accepted in wait lists)
Require numbytes > 0 in enqueueRead/Write/Copy (as in OpenCL 1.2)
Add region bounds validation in enqueueCopyBuffer
Added internal WebCL state object.
Merge branch 'master' into asyncworker
Throw INVALID_OPERATION if certain functions are called from WebCLCallback.