demandload: implement __call__
demandload can now load functions and classes, and not just modules.
(So if you access foo() rather than just foo.* it still works).
demandload still doesn't work for constants.
port:4:export
port:4:vaportight
port:4:import/export
FIXME: history is wrong here
port:1:1:-:eggs:import
port:1:2:+:eggs:vaportight
port:1:3:+:eggs:import/export
port:0:2:+:spam:export
port:0:1:+:spam:import
port:4:import/export