It was decided during VDD15Q3 but this change didn't make it before the
4.1.0 release. It is kept in the 4.1 series but documented as deprecated
and can now be retired as discussed during VDD15Q4.

With a minor tweak so that running `make lcov` is enough, rather than
the original `make check-code-coverage`:

   ./autogen.sh
   ./configure --enable-code-coverage
   make lcov

Closes #1891

Most of it is rescued from the old Trac wiki.

I shouldn't rely on auto-complete too much, especially for only two
characters...

Spotted by @fgsch

It also applies for the 4.1 and 4.0 series.

Refs #1890

Fixes #1889.

Raise a ParseError exception if not.

Fixes #1885.

When ESI delivering a gzip'ed object, emit the GZIP header+tail
precisely if no parent ESI has done so.

Fixes:	#1878
Testcase by:	fgs

When varnishtest creates a socket barrier, it will bind a socket and
listen to incoming connections. Once the number of expected connections
is open, connections are closed.

Barrier users only need to connect to the socket, read "nothing" and
block until the connection is closed. It allows virtually any process
to sync with varnishtest. The barrier will provide macros with its
socket information.

This is similar ASSERT_CLI, in order to make socket barriers creation
thread-safe.

All usage of cyclic semaphores has been replaced by non-cylic barriers,
except in the disabled test r01252 that absolutely needs one. It still
passes when run with the proper requirements.

This is useful in HTTP loops where it's impossible to predict and use an
array of barriers. All cycles expect the same number of waiters, unlike
semaphores.

They work like semaphores, except that they need explicit initialization
and can optionally be shared between processes.

This fixes a problem when a backend replies with 304 Not Modified
(after a http conditional request from varnish) and does not supply a
header that was duplicate in the cached object.

Before this patch, varnish would only supply (by copying from the
expired object) the first instance of a duplicate header.