- New Query methods: query.label(name), query.as_scalar(),

- New Query methods: query.label(name), query.as_scalar(),
return the query's statement as a scalar subquery
with /without label [ticket:1920];
query.with_entities(*ent), replaces the SELECT list of
the query with new entities.
Roughly equivalent to a generative form of query.values()
which accepts mapped entities as well as column
expressions.