[Bug 1874] See who's in a particular custom filter when posting

Conflicts:
	htdocs/js/jquery.postform.js
[Bug 1874] improved query methodology, closed some security holes and
added some error/sanity checking.  Also now sorts the final list.
removing superfluous <div>
(bug 2288) move checkforusername to routing

This wasn't a true __rpc_... endpoint, now it is
(Bug 4176) Support notifs should include username

Notifications of new support requests now contain the username or
(for logged-out requests) name provided by user. Notifications of
follow-ups to support requests now contain the username of the
person who left the response. I do not allow for anonymous follow-
ups because as far as I can tell they can't happen.
Merge pull request #455 from woggy/thisisatestbranch

[Bug 1874] See who's in a particular custom filter when posting
Merge pull request #466 from anall/feature/bug2288-checkforusername

(bug 2288) move checkforusername to routing
Merge pull request #427 from kaberett/bug4176-support-username

Bug4176 support notifications should include username
(bug 4907) Enable redirection for ios homescreen icons in S2

Added configuration instructions in doc/config-local.pl.txt
with commented-out version which works with current dw install.
Header linkref for ios homescreen icon is added if config
variable is present in any page served through S2.
Merge pull request #465 from dwmc15873/bug4907-ios-icon

(bug 4907) Teach S2 to serve up icons for iOS
(Bug 5154) Only print the multiform start if we have comments

Fixes a non-matching form tags issue
Merge pull request #467 from afuna/logout-bug5154

(Bug 5154) Only print the multiform start if we have comments
(BUG 4758) 32 themes for Librarian's Dreams - corrected number of themes in commit message
(Bug 4733) Mobility layout plus two themes

Layout by branchandroot. Child of Tabula Rasa
Suitable for mobile or desktop viewing

Several commits squashed into one
Merge pull request #445 from wahiaronkwas/bug4758-libdream-themes

(BUG 4758) 31 themes for Librarian's Dreams by Nornoriel and Musyc, with...
Merge pull request #468 from LivredOr/4733_Mobility_layout_3

(Bug 4733) Mobility layout plus two themes
(bug 5149) allow network-rel URLs in YT embeds

Youtube has started using network-relative URLs in its embed codes, eg
src="//www.youtube.com/...". This is a legit but uncommon syntax --
it means "fetch this location, using the same protocol as you used for
this page" -- eg http for http, https for https.

This patch updates the allow_iframe_embeds hook to permit URLs of this
form. Unfortunately, the URI module can't cope with them, so we have
to lie to it about the URL scheme to get the rest of its parsing to
work. We don't modify the URL that's actually used to do the
embedding, though -- just what's used for checks inside the hook.
(bug 5149) recognize network-relative URIs from YT

Tweak the URI-matching regex to recognize either a scheme of http,
of https, or a schemeless network-relative URI (starts with //)
when it is coming from Youtube.
Merge pull request #470 from rickscott/bug5149-youtube-embed-rel-urls-into-1.16

(bug 5149) allow network-rel URLs in YT embeds
Merge pull request #471 from rickscott/bug5149-youtube-embed-rel-urls-a11y

(bug 5149) recognize network-relative URIs from YT