pdf table wrap error in extension spec

[bashbaug]

Asciidoctor has a problem generating PDF output when a table cell does not fit onto a page, and a table in the OpenCL extension spec is exposing this problem.

The problem can be identified with the OpenCL spec toolchain via an error from optimize-pdf:

/home/bashbaug/git/OpenCL-Docs/config/optimize-pdf out/pdf/OpenCL_Ext.pdf
   **** Error: File did not complete the page properly and may be damaged.
               Output may be incorrect.

The problem appears to be caused by the cl_khr_extended_async_copies spec and I do not see the error if I comment out this spec.

The HTML specs are not affected. Still, we should fix this problem before the next spec release.