Changes to VCL

All VCL Objects should now be defined before used
- in particular, this is now required for ACLs. The error message for ACLs being used before being defined is confusing - see PR #2021::
  
  Name <acl> is a reserved name
VCL names are restricted to alphanumeric characters, dashes (-) and underscores (_). In addition, the first character should be alphabetic. That is, the name should match "[A-Za-z][A-Za-z0-9_-]*".
Like strings, backends and integers can now be used as boolean expressions in if statements. See vcl(7) for details.
Add support to perform matches in assignments, obtaining a boolean as result::
```
  set req.http.foo = req.http.bar ~ "bar";
```
Returned values from functions and methods' calls can be thrown away.

backends


* Added support for the PROXY protocol via ``.proxy_header`` attribute.
  Possible values are 1 and 2, corresponding to the PROXY protocol
  version 1 and 2, respectively.

vcl_recv

Added return (vcl(label)) to switch to the VCL labelled label.
The rollback function has been retired.

vcl_hit


* Replace ``return (fetch)`` with ``return (miss)``.

vcl_backend_*

Added read access to remote.ip, client.ip, local.ip and server.ip.

vcl_backend_fetch


* Added write access to ``bereq.body``, the request body. Only ``unset``
  is supported at this time.

* We now send request bodies by default (see
  :ref:`whatsnew_changes_5.0_reqbody`). To keep the previous behaviour
  add the following code before any ``return (..)`` statement in this
  subroutine::

	if (bereq.method == "GET") {
	    unset bereq.body;
	}


vcl_backend_error

Added write access to beresp.body, the response body. This may replace synthetic() in future releases.

vcl_deliver


* Added read access to ``obj.ttl``, ``obj.age``, ``obj.grace`` and
  ``obj.keep``.

vcl_synth
~~~~~~~~~

* Added write access to ``resp.body``, the response body. This may replace
  ``synthetic()`` in future releases.

Management interface
====================

* To disable CLI authentication use ``-S none``.

* ``n_waitinglist`` statistic removed.

Changes to parameters
=====================

* Added ``ban_lurker_holdoff``.

* Removed ``session_max``.  This parameter actually had no effect since
  4.0 but might come back in a future release.

* ``vcl_path`` is now a colon-separated list of directories, replacing
  ``vcl_dir``.

* ``vmod_path`` is now a colon-separated list of directories, replacing
  ``vmod_dir``.

Other changes
=============

* ``varnishstat(1)`` -f option accepts a ``glob(7)`` pattern.

* Cache-Control and Expires headers for uncacheable requests (i.e. passes)
  will not be parsed.  As a result, the RFC variant of the TTL VSL tag
  is no longer logged.