Handle foreign data in U. F. O..

This uses the PyTuple, which has no matching entity in X. M. L., as a special container for unrecognized data in python_persistent, allowing FontForge to round-trip that data in the top-level lib.plist and in the lib data for individual glifs.

When logging errors, how easy would it be to add the glyph name (or glif file name) - it would make finding problems far easier...