imagespeed_test improvements: refactor, and add tests of image iteration speed. We compare pointer arithmetic, versus getchannel(), versus IB::Iterator, and for each of those for loaded versus cached images.
imagespeed_test improvements: refactor, and add tests of image iteration speed.
We compare pointer arithmetic, versus getchannel(), versus IB::Iterator,
and for each of those for loaded versus cached images.

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