Truncate %D varnishncsa format specifier to an integer value.

This follows the format Apache logs in.
Exclude vcl_var since it is included in vcl.rst.
Add missing returns, and do a bit of cleanup
req.backend -> req.backend_hint
Forgot to commit the test-case
Allow ACLs to be unreferenced when vcc_err_unref=off.

Add a reference from the init function to any non-anonymous match_acl_*()
functions to ensure the compiler does not barf.

Fixes	#1504
Add a debug.no_backend() function to simulate a director failing to
pick a backend.
Directors are allowed to fail to pick a backend.

Fixes	#1501
White-space fix
White space fixes
Remove duplicate command line arguments.

We don't need to add the RST2ANY_FLAGS arguments twice.
Copy from source where the file exists.

With parallell builds, building this file has usually not happened yet
in the build directory.

Suggested by: Martin
Don't package build/doctrees in tarball.

These are just intermediate files written by Sphinx to
build the HTML documentation. We don't need to distribute
them.
Remove any superflous non rst/html from tarball.

When we in the future introduce something new and shiny here, don't
automatically start putting it into the tarball release.

This may seem a bit backward, the main idea is to avoid hardcoding
the section/subdirectory names yet another place.
Reduce contention on the wstat_mtx marginally while we figure out
what the real solution is going to be.
Stabilize a race in this test with some small delay
Move the wthread_stats_rate check into the threadpool, so that it
also takes account of fetch jobs.
Move the stat-summing from WRK to Pool where it mostly happens.
The mutex protecting summing of stats into the global VSC counters
is a contention point and scales negatively with number of thread-pools.

Sum into a per-pool dstat structure instead, and have the first
idle thread summ that into the global counters without blocking the
pool mutex.

Fixes	#1495

(I hope)
Properly complain if people try to reuse symbols.

Fixes #1510