implement schema_base_class for dynamic schemas

implement schema_base_class for dynamic schemas

Implement schema_base_class and schema_components support for dynamic
schemas at 'connection' time.

Augment btilly's test to check that schema_components are also applied
at 'connection' time.

This requires a rather horrible hack in ::Loader::connection, because
mro cannot normally deal with a changing @ISA inside of a call chain,
but it works.