- calling corresponding_column with keys_ok matches columns on name, not key, since

- calling corresponding_column with keys_ok matches columns on name, not key, since
the name is meaningful with regards to SQL relationships, the key is not
- adjustments to the recent polymorphic relationship refactorings, specifically
for many-to-one relationships to polymorphic unions that did not contain the
base table [ticket:439].  the lazy/eager clause adaption to the selectable
will match up on straight column names (i.e. its a more liberal policy)
- lazy loader will not attempt to adapt the clause to the selectable if
loads_polymorphic is not enabled, since the more liberal policy of adapting
columns fails for more elaborate join conditions
- will have to see if ppl want to do complex joins with polymorphic relations...
may have to add "polymorphic_primaryjoin" in that case as a last resort (would make
working around these issues a snap, tho...)