Add #ifdef 0'ed code to put another thread on body-fetching

Hugely inpired by patches from:	martin

Improve error reporting at the same time.

Fixes	#1100

for us in a single place.

Mostly by:	martin

pointer, in order to not have dependency between trouble entry and
objhead lifetime.

Fixes	#1091

Add accept-filter param which controls if we attempt kernel
filteringer.

Apply filters after listen() when we do.

Report failuers with VSL(SLT_Error)

Disable filters in pipe-lining test-case.

Fixes	#1101

Submitted by:	DocWilco

the original requester.

Submitted by:	DocWilco

- mention vmod_std(7)
- HEADER is released and used by vmod_std(7) so put it in its own line.
  The explanation is still needed though.
- for consistency replace leading tabs with spaces
- *fallback* are not strings so avoid mentioning the type
- use ascii characters in vmod_std(7)

And a few style changes from me to vmod_std.rst

Requested by: Federico G. Schwindt <fgsch@lodoss.net>

Reduce stacksize to 32k.