Prepare for moving idle events to class Partition.  Right now, it's
just a wrapper for idle_add().

Lists files and directories.  Supports storage plugins.

A SimpleDatabase instance can now "mount" other Database instances at
certain locations.  This is used to use a new SimpleDatabase instance
for each storage mount (issued with the "mount" protocol command).
Each such instance has its own database file, stored in the directory
that is specified with the "cache_directory" option.

Add the new idle event to Idle.hxx/Idle.cxx.

This commit adds the NeighborPlugin API which can be used to detect
nearby file servers that can be used by input plugins.  This list of
servers is exported using the new "listneighbors" command.  The idle
even "neighbor" notifies interested clients when a new neighbor is
found or an existing one is lost.

There's a lot missing currently: protocol&user documentation, and a
way to "mount" remote servers into the music database.  Obviously,
some code from the UPnP database plugin can be moved to a neighbor
plugin.

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

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

Based on the APE reader.

Don't call g_error(), which will abort the process and dump core.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

Renamed functions.

This is a rather huge patch, which unfortunately cannot be splitted.

Instead of using our custom ioops.h library, convert everything to use
the GLib main loop.