free slots, one for the data we want to write and one for the
end of chunk bits.

Fixes: #2207

inside struct ws.

clear that you are not supposed to use them as pointers.

Spotted by coverity.

While here rearrange variables to be more consistent.

Links to on the form https://www.varnish-cache.org/trac/ticket/<num>
are now https://github.com/varnishcache/varnish-cache/issues/<num>, at
least near the top.

Headings starting with "Changes since" looked redundant, and has been
removed. The result is a slightly more consistent changelog.

with the frame length.

Spotted by: Coverity