In load_inst(), when instantiating an instance the old way (i.e. when

In load_inst(), when instantiating an instance the old way (i.e. when
there's an __getinitargs__() method), if a TypeError occurs, catch and
reraise it but add info to the error about the class name being
instantiated.  This makes debugging a lot easier if __getinitargs__()
returns something bogus (e.g. a string instead of a singleton tuple).