Instead of instructing VUT authors to clean the generated files, make
sure they are automatically picked up. It is safe to upgrade while
still having the CLEAN_FILES rule in Makefile.am, despite "removing"
functionality (removing burden in reality).

Other improvements include a single Python detection even when building
several modules (but the underlying check is cached anyway) and a new
dependency to "nodist" sources for VMOD authors that follow the
recommendations. The "hardcoded" dependency is still present to avoid
breaking existing builds.

The file stevedore may return a buffer larger than asked for when
requesting storage. Due to lack of check for this condition, the code
to copy the synthetic error memory buffer from vcl_error would overrun
the buffer.

Patch by @shamger

Fixes: #2429

Make the subargument to -a select the overall protocol (PROXY/HTTP)
but, at least for now, not distinguish versions of these protocols.

Remove mention of http_CollectHdrSep().

So that part of the docs appear in the SYNOPSIS section.

DEFAULT is interpreted as LOWER for the HEX and URL encodings, and
is the only legal value for all other encodings.

and let that check if another function is desired.

syslog-ism "%m" being used in vsnprintf() via VSB.

That said, it would have been damn convenient of %m was also usable
in *printf(3)...

We seem to have most of it.

server.identity is not a new VCL variable.

Like $Event, $ABI has the effect of making generated docs until
the next $-directive disappear.