The Naim Uniti does not appear to support icecast-style streaming of FLAC
music but does support the codec from a DLNA server. This change looks for
"transferMode.dlna.org: Streaming" in the HTTP request header and responds
with something the Uniti (and hopefully other DLNA clients) accepts.

The only difference in the DLNA streaming mode is the reponse header and
that icecast metadata is disabled. If a client request indicates both modes
are supported, the DLNA mode is preferred (as the Uniti says it supports
both but then rejects a FLAC ICY stream).

Note: This change may be specific to Naim equipment (the only device it was
tested on). E.g. the hardcoding of Content-Length which works but is not a
logically correct value. The change should be backwards-compatible, so
only those clients requesting a DLNA stream will see any difference.

The server_socket library (used by the httpd output plugin) didn't
check for WIN32, that's fixed now.

This warning should only be logged when we really received something.
When the client disconnects, G_IO_IN is triggered, and the read
returns G_IO_STATUS_EOF.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

Drop the required GLib version from 2.16 to 2.12, because many current
systems still don't have GLib 2.16.  This requires several new
compatibility functions in glib_compat.h.

Accidently, MPD has been using several GLib 2.16 functions for a
while, and nobody noticed yet.  To simplify the code base, let's bump
the minimum GLib version for MPD to 2.16.  That version is old enough,
and it's reasonable to expect users to have it.

There's no reason to send both encoder tags and Icy-Metadata to the
client.  Let's disable Icy-Metadata when the encoder supports embedded
tags.

Plain "bool" consumes only one byte instead of four.

In HTTP, header names are case insensitive.

[mk: folded with patch "Put icy related functions in extra source
files"; moved icy_server.c from HAVE_CURL to ENABLE_HTTPD_OUTPUT;
removed an unused variable]

Due to a race condition, httpd_client_out_event() could be called even
when its GLib event source was already removed.  Check that case.

When the httpd output is cancelled, it freed all pages, but didn't
remove them from the queue.  Call g_queue_clear() and remove the
write source id.

Let's get rid of the "shout" plugin, and the awfully complicated
icecast daemon setup!  MPD can do better if it's doing the HTTP server
stuff on its own.  This new plugin has several advantages:

- easier to set up - only one daemon, no password settings, no mount
  settings
- MPD controls the encoder and thus already knows the packet
  boundaries - icecast has to parse them
- MPD doesn't bother to encode data while nobody is listening

This implementation is very experimental (no header parsing, ignores
request URI, no icy-metadata, ...).  It should be able to suport
several encoders in parallel in the future (with different bit rates,
different codec, ...), to make MPD the perfect streaming server.  Once
MPD gets multi-player support, we can even mount several different
radio stations on one server.