Enforce proper sequencing of world and kernel targets.

Enforce proper sequencing of world and kernel targets.

.ORDER: does *not* take an arbitrary list of targets of which all pairs
are supposed to be built in their specified sequence,
instead it specifies which adjacent pairs need to be built in sequence.
As a result, given a sequence "buildworld buildkernel quickkernel" and
the make targets "buildworld" and "quickkernel", make would still
parallelize the build of these targets.

Additionally, introduce quickworld to the sequencing.