While applying a relative spin scale adjusment (i.e., when dragging
from the lower half of the spin scale), wrap the pointer around the
screen edges (of the current monitor), so that the maximal possible
adjustment amount isn't artifically limited by the screen geometry.
This is especially useful for spin scales in dockables, since
dockables are normally placed near the edge of the screen.
When the mouse is released, move the pointer back to its initial
position (at the beginning of the drag), to allow for subsequent
adjustments.
Unfortunately, moving the pointer programatically isn't supported
on all envrionments (Wayland, Xephyr, ...), and worse yet,
detecting that the pointer failed to move is tricky, so we have to
resort to an ungly hack to maintain the current behavior in this
case. Gah :P
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