Makefile: Replace the m4 crock with a proper GNU Make crock.

The m4 was an unmaintainable pile of horribleness.  It needed
replacing.  The only question is: have I replaced it with something
even worse?

An important new feature of the Makefile is that we can be interested in
different zones in each view.  Previously, there was a list containing
the zones defined by the zoneset, and each view had to have the same
zones in it.  There's now a list ZONESET_all_ZONES containing zones
common to all views in a zoneset, but there's also a variable
ZONESET_VIEW_ZONES for the zones which are specific to each view.

We've also made the separation between preferred subnets and views
clearer.  Although we're still using the same names for both right now,
this will change soon.  There's now a list of preferred subnets for each
view, and the feature keyword has changed to :VIEW/name.

This is important because the new publication machinery will object if
we try to feed it zones which it doesn't know about.

We also drop the various dynamic zones from publication, because they
always had to be maintained manually anyway.