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This functionality is now provided by libxfce4ui, see commit
8990efaf "Use the spawn code from libxfce4ui."

Fix warning about m4 directory.

See https://bugzilla.xfce.org/show_bug.cgi?id=8930 for details.
Signed-off-by: Simon Steinbeiss <simon.steinbeiss@elfenbeinturm.at>

Loading over DBus is a tiny bit slower, but makes
it a lot easier to change values and also saves a
lot of hassle with modified properties.

Nearly all gtk 2.24 distros have 2.32 or newer, so
don't depend on 2.28 and use 2.30.

We already require GVFS for a trash implementation, so
why ot rely on the metadata storage too.