simplify the Model discovery method.
add doctoring to _get_subclasses_recurse, explaining how it's different to what exists for Model discovery.
changing the way select_subclasses works so that 'good' strings sidestep all the issubclass kerfuffle.
correcting comments
check that 'bad' input raises the right type of exception, with the right text.
test that a child model cannot reference a parent.
starting in on documentation.
more tests and refactorage.
Test that a Child object which also has an InheritanceManager cannot leak parents.
This isn't previously tested, but does also fail in < 1.6 as of master @ 8bead336a7fc12b48ee6541edfbfda13f021dba0