Please replace this commit with a better solution, if you have one.

e1ac5933 brought us the VRBT node
color encoded in the lower two bits of pointers.

gcc strict aliasing rules (as enabled with -O2 and higher) forbid
aliased lvalue access as in the following macro expanded code:

(*(uintptr_t *)&(parent)->entry.rbe_parent) &= ~((uintptr_t)3);

Until we have a better solution, disable strict aliasing with gcc
for targets with any source file using vtree.h.

Note that we would want to limit -fno-strict-aliasing to individual
compliation units, but automake does not offer a simple and clean way
to achieve this:

https://www.gnu.org/software/automake/manual/html_node/Per_002dObject-Flags.html

... and document it

The size of 1 for the p array would not be required, it is a safety
measure only.

we only use one passed and one piped requests, so our servers should
only ever see two requests.

Motivated by a failure on fedora armv7hl, which I do not understand:

**   c1    === txreq -url /1 -hdr "pipe: true"
**** c1    txreq|GET /1 HTTP/1.1\r
**** c1    txreq|pipe: true\r
**** c1    txreq|Host: 127.0.0.1\r
**** c1    txreq|\r
**   c1    === rxresp
**** dT    3.832
**** c1    rxhdrlen = 0
---- c1    HTTP header is incomplete
**** dT    3.833

Restructured so that:

* 'Upgrading' is limited to work that has to be done to upgrade from
  a current deployment to the new version.

* 'Changes' is a comprehensive, user-level description of changes and
  new features.

Conflicts:
	doc/sphinx/whats-new/index.rst

Committer Edit:
	Added Copyright header by example of
	fe8cfe84 and
	93439884

Noted by Simon Vikström, thank you

Closes #3551

The order matches the order of commits, except where I thought it made
more sense to join topics into contiguous sections.

We can incorrectly reference resp.reason from other sources when
jumping into vcl_synth. This also covers passing in a reason in
vcl_backend_error.

Provide a set of predictable subroutines that will be called by the
built-in vcl. Only transactional built-in subroutines are concerned,
which excludes vcl_init and vcl_fini.

Closes #3548

Better diff with the --word-diff --ignore-all-space options.

When it was in its own file it worked fine...