Summary:
- indicate location of OmegaConf.structured failures
- split the data gathering from enable_get_default_args to ease experimenting with it.
- comment fixes.
- nicer error when a_class_type has weird type.
Reviewed By: kjchalup
Differential Revision: D39434447
fbshipit-source-id: b80c7941547ca450e848038ef5be95b7ebbe8f3e