Some compilers are very picky, but we really aren't interested in the
return value.

Make sure we get a UTF-8 encoded string.

Parses CUE data from the "CUESHEET" tag.  Needs further integration in
the update thread.

The new method pair() receives an arbitrary name/value pair.  Support
for this is being added to a few decoder plugins.

Pass a callback table to scan_file() and scan_stream(), instead of
returning a tag object.

Didn't compile on GLib < 2.16.

This is easier and more efficient to loop on, because only two
variables get modified (src and dest).

The other audio_format attributes are not used.

In a C file, that is too late, because _mingw.h defaults to 0x0502,
and ours would be illegal redefintion.

Needed for the I/O thread.

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.

Provide _lock() and _unlock() to wrap all accesses from the mixer
plugin.

Use these instead of exposing the internal roar_t struct.

Add GMutex, GCond attributes which will be used by callers to
conditionally wait on the stream.

Remove the (now-useless) plugin method buffer(), wait on GCond
instead.  Lock the input_stream before each method call.  Do the same
with the playlist plugins.

To check for errors without reading.  The decoder thread wants to do
that, before it passes the input stream to the plugin.

Needed for the I/O thread.

config_add_block_param() cannot fail, which makes it easier to use.

.. and destruct the output object properly in test/run_output.

Clean up the process before exiting.

To demonstrate the new I/O thread.  libsoup is well-integrated into
the GLib main loop, which made this plugin pretty easy to write.

As a side effect, we have to initialize the I/O thread in all debug
programs that use the input API.