Intel extensions have been moved into cl_ext.h

[pcolberg]

#62 introduced new warnings, e.g.,

 In file included from ../include/acl.h:12,
                 from ../include/acl_hal_mmd.h:22,
                 from ../include/acl_bsp_io.h:12,
                 from ../src/acl_bsp_io.cpp:5:
../include/CL/cl_ext_intel.h:19:105: note: #pragma message: The Intel extensions have been moved into cl_ext.h.  Please include cl_ext.h directly.
 #pragma message("The Intel extensions have been moved into cl_ext.h.  Please include cl_ext.h directly.")