return proper symbol when add addon (bnc#878997)
Do not create end-less loop in add-on dialog (bnc#878997)

Reason why it is not possible to hide checkbox is that after first
addon user still can add more of them, but he must have way how to
end in next cycle and not checking checkbox is exactly this way.
release
Merge pull request #14 from yast/fix_sequencer

Fix sequencer