become an externally usable package but still remains within the main sqlalchemy parent package.
in this system, we use kind of an ugly hack to get the noseplugin imported outside of the
"sqlalchemy" package, while still making it available within sqlalchemy for usage by
third party libraries.

- modify inspection system:
	1. raise a new exception for any case where the inspection
        context can't be returned.  this supersedes the "not mapped"
        errors.
        2. don't configure mappers on a mapper inspection.  this allows
        the inspectors to be used during mapper config time.  instead,
        the mapper configures on "with_polymorphic_selectable" now,
        which is needed for all queries
- add a bunch of new "is_XYZ" attributes to inspectors
- finish making the name change of "compile" -> "configure", for some reason
this was only done partially