The "name" attribute is set on :class:`.Index` before the "attach"
events are called, so that attachment events can be used to dynamically
generate a name for the index based on the parent table and/or
columns. [ticket:2835]
The ``default`` argument of :class:`.Column` now accepts a class
or object method as an argument, in addition to a standalone function;
will properly detect if the "context" argument is accepted or not.
- fix bug due to regression from #2793, make sure we only go to load
scalar attributes here and not relationships, else we get an error if there's no
actual scalars to load
use accepts scalar loader here so we deal with _ProxyImpl correctly