a new VCL program initializes of finishes.

This also gives access to a per-VCL private void* which can be passed
as a hidden argument to the member functions.

If modules hold any global state, they should use the meta function to
keep track of when the last VCL program finishes and clean up their
internal global state then.



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5166 d4fa192b-c00b-0410-8231-f00ffab90ce4