- Fixed bug in foreign key autogenerate where if the in-Python table

- Fixed bug in foreign key autogenerate where if the in-Python table
used custom column keys (e.g. using the ``key='foo'`` kwarg to
``Column``), the comparison of existing foreign keys to those specified
in the metadata would fail, as the reflected table would not have
these keys available which to match up.  Foreign key comparison for
autogenerate now ensures it's looking at the database-side names
of the columns in all cases; this matches the same functionality
within unique constraints and indexes.
fixes #260