Fix pg_dump so that comments on views are dumped in the proper sequence.

Dump the alignment and storage information for user-defined types (how'd
that manage to slip through the cracks?), and don't dump 'shell' types
that don't have typisdefined set.  Fix badly broken logic for dependencies
of type definitions (did not work for more than one user-defined type...).
Avoid memory leakage within pg_dump by being more careful to release
storage used by PQExpBuffer objects.