Optionally convert all imported (not XCFs) images to 32 bit linear
floating point, and optionally add a little noise in order to
distribute the colors minimally. The new options are on a new "Image
Import & Export" prefs page that needs a new icon. Original dithering
patch by pippin.
For conversions that have no dither options (like RGB -> GRAY or u8 ->
u16), always preserve text editability, for conversions that have
dither options (like RGB -> INDEXED or u16 -> u8), give the user the
choice whether to enable dithering.
Michael Natterer