The original mkisofs would only care for the proper ISO9660 image
but we've switched to xorriso which is able to perform the hack
to yield UEFI hybrid images; thus no need for the postprocessing.

Requires mkimage >= 0.2.5 and xorriso (obviously).

Here we go with postprocessing priorities along the way
as ISO hybridization has to occur before implanting
final MD5 sum (which must happen earlier than e.g. some
external MD5SUM file generation).

Unfortunately proper dependencies aren't applicable here
(though I'd like to be proved wrong on this one).

Please note that this needs propagator > 20101130-alt9
for automatic mode to work (has also been worked around
in gfxboot case with design-bootloader-source-6.0-alt1).

Thanks rom_as@ for asking about the hybrid image status
and helping out with testing.