the number of bytes in the workspace.

This is the most obscure test-case I have written so far, and I wonder
how portable it is.  I may have to drop it if it does not work on
systems with different width/alignment requirements.

Fixes: #693



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4830 d4fa192b-c00b-0410-8231-f00ffab90ce4