Currently, selecting a single dive or deselecting all dives was
quite awkward: One had to pass in a single-dive vector and the
dive itself (as current dive). Provide a convenience function
that selects a single dive or deselects all dives if null is
passed in.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
f4f9ba9263