.. and move the plugins to src/encoder/plugins/.

Users now have to call Close() explicitly.  This simplifies using the
class, as most users have automatic socket management already, and
Steal() had to be used often.

This call is not thread-safe.

Fixes more thread-safety bugs.

Add a Page queue to class HttpdOutput, and use DeferredMonitor to
flush this queue inside the IOThread.  This fixes a thread-safety
issue: much of EventLoop is not thread-safe, and the httpd plugin
ignored that problem.

Do all I/O in the IOThread and not in the main thread.  This solves an
upcoming deadlock problem.

Don't let the server care for client problems.

Don't iterate the std::list each time.

No GLib memory allocation.

On OSX, the configure-flag --enable-osx is used to enable the
unsupported osx output. It sets the HAVE_OSX preprocessor define.

src/output/OpenALOutputPlugin.cxx uses this define to determine wether
it is building on OSX, and imports different headers (which have
nothing to do with the osx output) depending on wether or not it is
set.

See code comment.

Map LogLevel::INFO to G_LOG_LEVEL_INFO, and LogLevel::DEFAULT to
G_LOG_LEVEL_MESSAGE.  Now client connect/disconnect message are only
logged on log_level "secure".

Some, or most, Win32 audio players will pass "icy-metadata:1" to
streaming servers. MPD expects a space between ":" and "1" at this
point, and thus does not send any stream metadata. This applies to
foobar2k and Winamp, for example.

According to forums.radiotoolbox.com/viewtopic.php?t=74 not having
a space there is expected behavior, so maybe MPD could accept
both forms to determine if metadata should be sent or not.

Replaces GLib's g_ascii_strncasecmp().