- "not equals" comparisons of simple many-to-one relation

- "not equals" comparisons of simple many-to-one relation
to an instance will not drop into an EXISTS clause
and will compare foreign key columns instead.

- removed not-really-working use cases of comparing
a collection to an iterable.  Use contains() to test
for collection membership.

- Further simplified SELECT compilation and its relationship
to result row processing.

- Direct execution of a union() construct will properly set up
result-row processing. [ticket:1194]