tests/test-ro-message.out

rewrite demandload module to be more flexible.
performance not affected.

old demandload module could only import top-level modules like os and
sys.

with rewrite, all of following syntax is emulated perfectly:

import foo, bar                    foo bar
import foo.bar.quux                foo.bar.quux
from foo.bar import quux, blurfl   foo.bar:quux,blurfl

only thing missing is "import foo as bar".

also, namespace clashes between placeholder object and demand loaded
module are no longer possible.

abort: Permission denied - test-ro-message/b/vehicle