* remember push errors in the context
* also fail additional pushes once we saw an error

Try to fail requests as early as possible. Otherwise just calling VDP
functions after an error is a noop.

Fixes #2618

suncc implements the inline functions from cache.h using it

This includes building the fuzzer to avoid code rot, but exercising
the fuzzer will be done elsewhere.

No need to remain paranoid when the actual root case is dead
simple (see previous commit)

This reverts commit f5ce5516.

Ref: #2645

As WS_Reset() clears the overflow marker, the correct order for
resetting and marking an overflow is WS_Reset(); WS_MarkOverflow();

Fixes the last seemingly obscure bit of #2645

If vbf_default_filter_list() returned without anything written to
the vsb (for no body or length 0), we would return as the filter
list whatever existed at ws->f + 1 prior to calling VBF_Get_Filter_List
(for example the string logged with std.log()).

Consequently, backend requests would fail with

	FetchError     Filter '...' not found

stuff there.

issue a membar to ensure that the overflow marker is written
before a failing WS allocation returns and is thus visible from
a different context.

pan_ic() already has an implicit membar via the mutex lock.

Ref #2645

list of VCLs" vs. "Do things with VCLs on list"

Ref: #2645

Spotted by:	slink

Should we plan to phase out synthetic() ?

Thank you to @martin-uplex for the review