Relation editor "creeps"

[AM909]

When you create a new relation from the "list of all relations" window by clicking the "+ gear" button, the position of the window moves down and right each time you do so, regardless of whether you have closed any previously opened windows.

This "cascade" effect is normally reserved for when you bring up multiple windows at the same time, so as to leave the title bar of the previous window visible.

This is undesirable because it forces the user to move the window more often, particularly on a crowded desktop.

I believe this effect only appeared in the latest tested release (i.e. it was not in 3094).

[bastiK]

(In [3200]) fixed #4930 - Relation editor "creeps"