Fixes #2617

Instead of allocating struct h2_sess out of the same workspace that is
used as our rxbuffer, we rather keep it on the stack in h2_new_session.

If the size of the initial h/2 request payload is close to half the size
of the workspace, we would end up exhausting the workspace in HTC_RxInit
after allocating our h2sess struct.

Spotted by Federico G. Schwindt

Fixes: #2619

Ref #2645 but cannot be the cause because workspace is just not
overflowed

Doesn't change the logic however.

Hopefully this...

Fixes	#2605

... to save stack space

Fixes #2643

Ref #2643

Yes, I know, this is far from perfect, but it does not require
any changes outside the signal handler and will hopefully simplify
error report handling significantly.

Ref #2643

Spotted by:	fgs

purports to say on the tin, and by removing the quantum-test
it trips over.

better sense of it now.

Ref #2622

running the transaction.

almost certainly an error, so make it one.

Fixes #2613

fixes #2639

Not real ids; for consistency with the other platforms.

note on jail_solaris:

ideally, vmods could tell the jails about privileges they require, but
for now (and because vmod_unix lives in varnish-cache), just add the
required privilege to the permitted set.

I have also considered the option to add additional privileges via the
-j argument (and actually would still want to add that somewhen), but
for this purpose, varnish should really DTRT by default.

note on priv_allocset:

Most of the sun folk had proven to be good interface designers, but
an API which requires dynamic allocation/deallocation really does not
play well with my efficiency fetish. So good we got library
constructors/destructors.

note on getpeerucred:

basically the same thing, but this time they at least added
ucred_size(). Not intended for use like this, but anyway....