updated OpenCL headers

[Trass3r]

> i just tested it to build on windows and it does not build at all (dmd  
> 2047):
>
> opencl\program.d(107): Error: forward reference to  
> 'CLObjectCollection(cl_device_id)'
> opencl\program.d(107): Error: CLDevices is used as a type

Yeah, the code depends on this patch:  
http://d.puremagic.com/issues/show_bug.cgi?id=4503
Gotta add this note somewhere.

If you compile it with a patched dmd, you should only get linker errors  
which are most definitely caused by the change of the calling convention  
in OpenCL 1.1.
As soon as Nvidia releases drivers for 1.1 I will update the OpenCL.lib  
import library.