Add std.rollback() to rollback req or bereq and mark the builtin rollback
as deprecated.

Original diff by Nils Goroll. Tweaks and reworked after phk comments
by me.

Fixes #1512

Un-static-fy vtc_maxdur

Fixes #1563

Reported by:	Meng Zhang

obj.{grace,ttl} are read-only.

Suggested by:	scoof

dedicated setup function we have.

Fixes	#1553

Fixes #1561

a '*' indicates that we are currently in the method.

Also add a list of methods we have previously called.

Spotted and fixed by:	Nils Goroll

Fixes #1562

that need to be purged we iterate until done.

Fixes #1551

For security reasons, we run the C-compiler in a sandbox process
which by default uses the same (non-)privileges as the other sandboxes
(VCL compiler, test-loader process and the worker process).

On some systems access to the C-compiler is limited, also for reasons
of security, and varnishd will fail to compile VCL code, unless all
the sandboxes are given access to the C-compiler.

Add a new parameter "group_cc" which adds a single gid to the grouplist
of the sandbox which executes the cc_command, for the benefit of such
systems.

Do some slightly related polishing of the docs/help-texts in this area
while here anyway.

Fixes #1521

Leave shm_reclen as a parameter alias for now.

Parameter vsl_buffer must be 12 bytes larger than vsl_reclen in order
to avoid a panic when we try to put 12 pounds of VSL into a 5 pound
vsl_buffer sack.   Tweak the opposite parameter Minimum or Maximum value
when we set one of of these parameters.

Fixes #1547

This reverts commit 78126742 since it broke master.

Fixes #1555

HTTP message.  Presently supported "req", "bereq", "resp", "beresp".

This is now possible because synth responses do not go through
deliver any more, as error responses used to.

Patch by:	Nils Goroll

Much appreciated