The dive-site-edit and dive-site-table tabs both put the filter
into a special dive-site mode. When switching between both, it
could happen that the one got its show befor the other got
its hide event.
Thus, the first would start dive-site filtering and the second
stop it. Now the app was not in filter mode even though it should.
To solve this problem, add reference counting for the filter's
dive-site mode. In both tabs call the enter/exit functions
on show/hide. In the dive-site-table tab, when the selection
changes, use a set function that doesn't modify the reference count.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
065423896d