#34 Update IDENTIFIER's to have "file:"

[Dan Mueth]

We need to go through the example packages
(gdp-example1 and scrollkeeper-example1, and probably
many existing OMF file which people will use as
examples) and set them up to use "file:" in their
INDENTIFIER's URL.

Basically this means fixing the sgmldocs.make and
htmldocs.make makefiles.

This can't be done until the bug w/r/t handling the
"file:" URI scheme is fixed.