vrt.h is required before vcl.h, which only contains the table
generated parts of the VRT api.

to the VDIR.

Refs 606d4856

Fixes #2433

Otherwise the VCL poker will eventually cool down the underlying VCL.

Fixes #2432

It leaks a bit outside the mgt_vcl_cooldown function but it's a trade
off to also avoid being too intrusive where go_cold is directly set.
The VCL poker now sets the state to COLD instead of indiscriminately
sending AUTO to all VCLs, only when the cooldown period has elapsed.

Refs #2432

Refs #2432

Refs #2432

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().