[Swan-dev] replace "make check UPDATEONLY=1" with "make update"

[D. Hugh Redelmeier]

| From: Paul Wouters <paul at nohats.ca>

| you often need to add FORCE=1 (I know you love these tweaks :)

I've not looked at any of the details, so this is just principle:
the polite way of telling make to do something is a target, not adding
definitions.

Not totally unrelated: I would like our scripts to work with
--warn-undefined-variables.  I know, I'm repeating myself.

FORCE=1 suggests the questions:
What does FORCE=0 mean?
What does FORCE=2 mean?
What does FORCE=no mean?