Add "black point", "grey point", "white point" and "auto" buttons to the curves dialog
Submitted by Rodrigo Severo
Link to original bug (#750951)
Description
The "black point", "grey point", "white point" and "auto" buttons available in the Colors >> Levels dialog should also be available in the Colors >> Curves dialog.
Users that prefer the Curves dialog instead of the Levels one should also have access to the functionalities provided by these buttons.
The functionality of these buttons on both dialogs should be the same.
Version: git master