[PATCH] handle old-style "root=" arguments

[PATCH] handle old-style "root=" arguments

When we changed try_name() to handle new-style printable dev_t formatting we
broke lots of people's setups.  Lilo, grub, etc.

Fix that by trying new-style formatting first, then fall back to old-style.

People should generally use new-style %u:%u major:minor formatting in the
future.