Fix rolequery unit test for PEP8.
Restructure TERule __str__

Eliminate instance check and try common case of getting perms; catch
exception for type_* rules case.
Raise exception for None being returned from qpol.

The C code returns NULL for cases such as getting the conditional for
unconditional rules.  The SWIG passes that up as None rather than
raising exceptions.

Update TERule for this change.
Implement ObjClass and Common classes.