Suggestion: add the ability to reverse the button effects on QAbstractSpinBox/QSpinBox

It would be useful to have the ability to reverse the button effects on a QAbstractSpinBox so that pushing the up arrow button or up arrow key would decrease the value and pushing the down arrow button or down arrow key would increase the value. As things stand now, QSpinBox explicitly prevents setting the singleStep property to a negative value or setting the maximum to be larger than the minimum.

While one can certainly reimplement stepBy() in a subclass to achieve this behavior, ideally this ability should be put (maybe a boolean property like "reversed" or something) on QAbstractSpinBox so that it would work for all QAbstractSpinBox subclasses. Then, for example, the meaning of stepUp() and stepDown() would be reversed, and stepBy() would not need to be changed.