Tiffs may misreport whether their pixels are stored as premultiplied (like in #1511, which breaks raster.input after 77e5858), or in the case of tiff read from gdal we have no way to know if pixels are premultiplied. For both these reasons we need a way for the user to control whether images need to be premultiplied before rendering/compositing. Will be useful for debugging future bugs too.
add 'premultiplied' property on raster symbolizer to allow user to co…
…ntrol (in rare cases) the premultiplied status of images in cases where tiffs mis-report it - closes #1512
update raster symbolizer test after 0972662 and #1512
whoop, not quite done here.., re-opened.
finish #1512 and adjust tests to use new parameter
done now closing.