Use the new uri_get_suffix() overload that removes the query string.

Make the "open" method of plugins "file" and "archive" dummy methods
that always fail.  Instead, let InputStream::Open() hard-code access
to these two plugins by using OpenLocalInputStream().  This allows
simplifyin the algorithm for falling back to probing archive plugins.

Replaces the method Close().

Don't use the mapper - all DetachedSong instances we get have already
been mapped.

For debugging.

Prepare for UPnP songs that retain there database identity.

From now on, struct Song will be used by the database only, and
DetachedSong will be used by everybody else.  DetachedSong is easier
to use, but Song has lower overhead.

.. instead of decoder_plugin_from_suffix().  This reduces overhead by
walking the array only once.

This commit adds the basic infrastructure for reporting bugs from
DecoderAPI.cxx via DecoderThread.cxx to DecoderControl.

Merge the two loops into one, and eliminate the GSList.

The new class Path only holds a string pointer without being
responsible for allocation/deallocation.  The FileSystem.hxx library
accepts Path arguments instead of AllocatedPath, to avoid forcing
callers to allocate another string object.