Reset the timer when paused and no client is connected.

This fixes Mantis ticket 0003527.

Wrap close(), use closesocket() on WIN32/WinSock.

Pass audio_output objects around instead of void pointers.  This will
give some more control to the plugin, and prepares for non-blocking
audio outputs.

Move the "extern" declarations from output_list.c, for more type
safety.

In the "vorbis" plugin, this is a copy of the old flush() method,
while flush() gets a lot of code remove, it just sets the "flush" flag
and nothing else.  It doesn't start a new stream now, which should fix
a few problems in some players.

Fixes build failure on WIN32.

This fixes the following valgrind warning occuring on the first call of
httpd_output_read_page:
==20124== Conditional jump or move depends on uninitialised value(s)
==20124==    at 0x425E65: httpd_output_read_page (httpd_output_plugin.c:240)
==20124==    by 0x426087: httpd_output_open (httpd_output_plugin.c:279)
==20124==    by 0x41D862: ao_open (output_plugin.h:206)
==20124==    by 0x41E133: audio_output_task (output_thread.c:590)

This cleanup call is obsolete, since we moved the binding code to
enable()/disable().

RFC 5334 10.3 defines the MIME type "audio/ogg".  We could use
"application/ogg" as well, but we know for sure that we only emit
audio data.

Added support for a new optional configuration setting for the httpd output
named "bind_to_address". Setting it to a specific IP address (v4 or v6) will
cause the httpd output to bind to that address exclusively. Supporting
multiple addresses in parallel is future work.

This implements the feature requests #2998 and #2646.

Work around aliasing warning.

Send silence to all connected clients while paused, to avoid
connection interruption.

Avoid buffer underruns on the streaming client, if the encoder is "too
efficient" (e.g. when encoding silence while paused).

libwrap support is in MPD but only for the control port.  This patch
adds support for the http port.  The code is copied from
src/client_new.c

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.

Changed the wrappers for pipe(), socket(), accept().  On WIN32, this
does not work for pipe().

Added the "fd_util" library, which attempts to use the new thread-safe
Linux system calls pipe2(), accept4() and the options O_CLOEXEC,
SOCK_CLOEXEC.  Without these, it falls back to FD_CLOEXEC, which is
not thread safe.

This is particularly important for the "pipe" output plugin (and
others, such as JACK/PulseAudio), because we were heavily leaking file
descriptors to child processes.

Implement the methods enable() and disable().  Bind the HTTP port in
the enable() method, but reject all incoming connections until the
output is opened.

The first patch by Patrick didn't work, because his "#ifdef HAVE_OSX"
line would have required config.h.

On Mac OS X, the httpd plugin cannot be compiled, because OS X's
system headers do nto include sys/types.h, although they use
u_int32_t.