Test suite modernization in progress. Big changes:

Test suite modernization in progress.  Big changes:
 - @unsupported now only accepts a single target and demands a reason
   for not running the test.
 - @exclude also demands an exclusion reason
 - Greatly expanded @testing.requires.<feature>, eliminating many
   decorators in the suite and signficantly easing integration of
   multi-driver support.
 - New ORM test base class, and a featureful base for mapped tests
 - Usage of 'global' for shared setup going away, * imports as well