Fix erroneous referral of sub-lattices as chains

I originally though the product of a flat lattice and any other lattice was a
lattice with a series of disjoint chains. This is incorrect, it's a series of
disjoint sub-lattices.

The algorithm works the same regardless.
Fix get-summaries and get-callers to respect information lattice

See the commit message of cfa2's 0160ee.