- [feature] New reflection feature "autoload_replace";

- [feature] New reflection feature "autoload_replace";
when set to False on Table, the Table can be autoloaded
without existing columns being replaced.  Allows
more flexible chains of Table construction/reflection
to be constructed, including that it helps with
combining Declarative with table reflection.
See the new example on the wiki.  [ticket:2356]

- [bug] Improved the API for add_column() such that
if the same column is added to its own table,
an error is not raised and the constraints
don't get doubled up.  Also helps with some
reflection/declarative patterns. [ticket:2356]