Make insertGlyph smarter.

[typesupply]

Don't create a new glyph and copy the data from the old glyph if all of these conditions are met:

1. The glyph does not belong to another object.
2. The glyph is an instance of exactly the destination object's defined class. Subclasses should not match.
3. The glyph does not have a notification dispatcher.

Add some documentation about all of this to the notes in the method.