link to credits for "PHP Group" (bug #67532)
Tighten up the wording on the Twitter link.
Add Twitter icon to the home page, linking to @official_php.

I've deliberately implemented this in such a way as to allow for further social
media buttons down the track if we want. I've also kept it intentionally
unobtrusive: it's there (previously, we only mentioned the Twitter account on
the mailing lists page, which was weird), but pretty subtle in the sidebar.

There's one additional dependency: a one glyph subset of Font Awesome (created
using Fontello) containing the Twitter icon. (Should we later want to include
other icons from Font Awesome, fonts/Font-Awesome/config.json can be fed back
into Fontello as a starting point.) The additional style sheet and font file
are cached correctly, and once loaded by the user, shouldn't need to be loaded
again, as with Fira Sans. On a cold page load, this adds two requests and just
under 3 kB to the page load.

I consider all of this reasonable, both technically and in terms of promoting
@official_php a little more, but I won't be terribly offended if someone wants
to revert this.
Attempt to fix the php.net cross-domain issues once and for all.

(But this is a terrible hac...)

ONCE AND FOR ALL.
Revert "Attempt to fix the php.net cross-domain issues once and for all."

This reverts commit d89cf4ec47214e5d2494ced23a732a8861695360.
Shift the social media block down so it doesn't look like Special Thanks.
5.6.0RC2 release announcement
Merge branch 'master' of https://github.com/php/web-php
Merge branch 'master' into php-uk

Conflicts:
	include/header.inc
redirect php.net/** to arithmetic operators page
update from official repository svn.php.net
Merge branch 'master' of https://github.com/php/web-php
Merge branch 'master' into php-uk