A priority should be a volatile thing: it should schedule a song for
playing back once, but it should not affect the next time the queue
gets played.

Empty currently, but code will be added song.

Fixes compiler warning.

This was used by proprietary software.  MPD adopted it a few years
ago, which turns out to be a mistake, because it now creates problems
for some MPD users (http://bugs.musicpd.org/view.php?id=4168).

Avoids crash because Close() invokes a call on a destructed
NfsConnection.

Avoid calling NfsConnection::RemoveLease(), because the lease has been
removed already.

Clean up the "state" to indicate that there is no longer any
asynchronous operation.  Fixes another NFS-related crash due to
cleanup of a non-existing asynchronous operation.

Avoids a crash that occurs when NfsConnection::OnSocketReady()
dereferences itself before returning.

During the NfsLease::OnNfsConnectionFailed() call, the old (defunct)
nfs_context may be used to close file handles.  Such code does not yet
exist, but will be added soon to fix other bugs.

Fixes potential second mount attempt after the old connection to the
NFS server was shut down.

libmp4v2 is licensed under MPL 1.1, which is incompatible with GPLv2.
Unfortunately, this means that we must remove the plugin.

More information can be found in the Debian bug report:

 http://bugs.debian.org/767504

Set the Error when zzip_seek()==-1 and not on success.  Fixes a crash
after seeking.

Broken by commit cdbdcec7

Android releases were missing since 0.19.1.

Simplify the definition of many build options.