Modernize IBA::compare -- take an ROI and nthreads, work for all data types.
IBA::computePixelStats -- make it work for all pixel types
IBA::isConstantColor -- modernize API, make it work with all types, with ROI.
Also add a unit test for it.
IBA:isConstantChannel -- modernize API, respect ROI, add unit test.
ImageBufAlgo::isMonochrome: modernize API, honor ROI, add unit test
IBA::fixNonFinite: modernize API, honor roi, parallelize.