triggering the building generator

[Seth Teller <seth@graphics.lcs.mit.edu>]

here's an end-to-end consideration:  how the generator should
be triggered to track updates in DOF's live campus database.

ideally, whenever DOF commits changes to the 2D data, we'd like
to produce faithful 3D generated data which tracks the changes.
here's something to think about:  can we do this as a sort of
polling makefile (perhaps literally), that periodically wakes
up and checks that each generated file is newer than its 2D
counterpart.  if not, regeneration is triggered.

periodically could mean every morning at 4am.  we could also
put a mechanism in place whereby the DOF guys could explicitly
trigger a build, if they've changed a lot of stuff and are 
impatient to see the results in 3D.

another question to think about:  where should this process run ?

prof. t.