responding to DNS requests.

…ection.

…tes and
  can continue byte by byte. Also it can continue after an interrupt.

…d struct.

  thread output.

…ion.

… rwlock.

  forward_add and forward_delete should be distributed to other processes,
  but when threaded, they should not be distributed to other threads because
  the structure is not thread specific any more.

… an rwlock.

…k calls.

…e failure.

* - fast-reload review, respip set can be null from a view.
* - fast-reload review, typos.
* - fast-reload review, keep clang static analyzer happy.
* - fast-reload review, don't forget to copy tag_actions.
* - fast-reload review, less indentation.
* - fast-reload review, don't leak respip_actions when reloading.
* - fast-reload review, protect NULL pointer dereference in get_mem
  functions.
* - fast-reload review, add fast_reload_most_options.tdir to test most
  options with high verbosity when fast reloading.
* - fast-reload review, don't skip new line on long error printouts.
* - fast-reload review, typo.
* - fast-reload review, use new_z for consistency.
* - fast-reload review, nit for unlock ordering to make eye comparison
  with the lock counterpart easier.
* - fast-reload review, in case of error the sockets are already closed.
* - fast-reload review, identation.
* - fast-reload review, add static keywords.
* - fast-reload review, update unbound-control usage text.
* - fast-reload review, updates to the man page.

- Merge #1042: Fast Reload. The unbound-control fast_reload is added.
  It reads changed config in a thread, then only briefly pauses the
  service threads, that keep running. DNS service is only interrupted
  briefly, less than a second.