Was doing clamping as fix for T42984. Seems we can ommit clamping for
sculpting if we make sure overlap is not zero with negative values.
Control for clamping is moved to the "Use Clipping" function of curves
(which is on by default), so both bugs remain squashed and advanced
users can now properly utilize curves in sculpting, though not all
brushes work well with negative curves.
Antonis Ryakiotakis
9f911f62dc