Drop execution permission on header files

These aren't meant to be executable
Use KHR ICD Dispatch structure

Add the relevant header for the ICD Dispatch extension.
Downloaded (with modifications) from
http://www.khronos.org/registry/cl/specs/opencl-icd-1.2.11.0.tgz
Add functionality to report API errors

This will help to diagnose invalid CL API calls
Add verbosity when API calls fail

This causes the runtime to report invalid arguments and when a command
fails for some reason.
Add more error API verbosity

We now report errors when the return code is returned via a integer
argument to function, even if that pointer is null.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/oclgrind/runtime.cpp
Revert "Use KHR ICD Dispatch structure"

This reverts commit aa40c4db0b7de8c2962e52f1faa439ece306122c.
Add option for API error reporting

This makes API error reporting disabled by default.
Merge pull request #58 from silverclaw/master

Add debug verbosity for erroring API calls