thunar-volman: add eject to RDEPENDS

Ejecting USB-memory stick caused:
Error starting job: Failed to execute child process "eject" (No such file or directory)

run-tested with angstrom/meta-oe environment on overo

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>