For out-of-tree utilities.

The corresponding symbols were already in libvarnishapi since 1.5!

When omitted, the callback defaults to printing to stderr and exiting
with the provided status.

With the exception of dispatch_f that already has a dispatch_priv.

This is a first step away from the global VUT symbol, handled outside of
VUT_Setup in preparation for the "unglobalization".

The API is responsible for checking that global options aren't used more
than once, despite it being handled (soon) in individual VUT setups.

This gives users a consistent usage/help message depending on whether
they run VUTs from the PATH or from a specific location. In order to
kill some of the redundancy, a VUT_InitProg macro does the $0 magic.

longer use this parameter any more.

autosizes everything.

We need it to build out-of-tree VSCs.

This reverts commit a1ac5e7e.

Redundant

Too many acronyms...

Since we seem to have a number of new VCL variables, there is now
a section heading for that in Upgrading.

Spottes by:	dridi

the shared memory segment could have gone away, simply
ignore the segment in that case.

Fixes #2411