[d-i] Please change yaboot-installer priority to standard

[Colin Watson <cjwatson@debian.org>]

For d-i to complete an installation on newworld powerpcs without too
much faffing around by hand, yaboot-installer needs to be installed by
default on subarchitectures where it's suitable. Now that
libdebian-installer does subarchitecture checking properly, could you
please change yaboot-installer's Priority: to standard so that this
happens?

Every other udeb that Provides: bootable-system is Priority: standard,
so this is consistent.

Thanks,

-- 
Colin Watson                                  [cjwatson@flatline.org.uk]