TaskQueuer: add missing doxygen comments
TaskQueuer: add missing doxygen comments

This should have been part of 75836364b31b0226de439e11c9c3ec4a9d8c03a0
(and a few subsequent commits).

Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui,Tarsnap/tarsnap-gui