Allow IB::Iterator ctr that takes an ROI to also take the 'unclamped' flag. Also some simplification of other constructors.
Allow IB::Iterator ctr that takes an ROI to also take the 'unclamped' flag.
Also some simplification of other constructors.

micler/oiio,OpenImageIO/oiio,micler/oiio,bdeluca/oiio,micler/oiio,mcanthony/oiio,mcanthony/oiio,bdeluca/oiio,sambler/oiio,OpenImageIO/oiio,YangYangTL/oiio,bdeluca/oiio,YangYangTL/oiio,cwilling/oiio,lgritz/oiio,sambler/oiio,scott-wilson/oiio,lgritz/oiio,lgritz/oiio,micler/oiio,scott-wilson/oiio,mcanthony/oiio,bdeluca/oiio,cwilling/oiio,sambler/oiio,lgritz/oiio,cwilling/oiio,OpenImageIO/oiio,mcanthony/oiio,scott-wilson/oiio,YangYangTL/oiio,OpenImageIO/oiio,YangYangTL/oiio,cwilling/oiio,scott-wilson/oiio,sambler/oiio