Invoke ${MAKESUMS} for ${RELEASEDIR}/${RELEASEMACHINEDIR}/installation files
as snap_md_post target in etc/etc.${MACHINE}/Makefile.inc rather than
as release target in distrib/${MACHINE}/Makefile so that builds for
release in distrib/${MACHINE}/Makefile don't have to be serialized.

XXX: maybe ramdisk kernels should be installed into binary/kernel dir
XXX: as other ports rather than installation dir, and
XXX: kernel config names should be preserved in their filenames.