SplitPane not passing correct orientation JSplitPane

[Sciss]

From scala/bug#7738

SplitPane is passing java.awt.Adjustable.HORIZONTAL and etc to JSplitPane, but the latter expects its own constants like JSplitPane.HORIZONTAL_SPLIT. In fact, these values aren't the same.

[Sciss]

I agree that this is wrong, but unfortunately we have always had this behaviour now. Arguably what is "horizontal" and what is "vertical" subject to interpretation, especially if it's 'vertical' and not 'vertical split'. I suggest thus to simply add a note to the documentation making this perhaps less intuitive difference more clear.