playlist_file_print() already handles stored playlists.  spl_print()
is never called with a successful result.

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

playlist_domain is no longer used for class Error.

This breaks on some standard library implementations.

Necessary to preserve type information.  The try/catch sequence didn't
work previously.

This compatibility hack was accidently broken by commit f072cbbb

memcmp() can overflow the buffer.