OverviewMap will break if moveend is triggered too early

[ahocevar]

Currently, the update() method of Control.OverviewMap is bound to the moveend event before the initial call of update(), which is there to create the overview map. In some occasions, if the moveend event is triggered before the initial update is finished, the overview map will break because createMap() will run twice at the same time.

The attached patch fixes this by registering update() for the moveend event after calling update() manually.

Note that this patch also removes the clickHandler deactivate/activate cycle, which is obsolete now that #1247 is fixed.

[ahocevar]

This is a duplicate of #1320 (sorry, must have clicked on submit twice accidently).