ALTER TABLE ... RENAME: minor stuff

This patch adds a missing heap_freetuple() to renamerel(), documents
the decision not to make renamerel() update the sequence name that
is stored within sequences themselves (thanks to Tom Lane), and adds
some rudimentary regression tests for ALTER TABLE ... RENAME on
non-table relations.

Cheers,

Neil

--
Neil Conway <neilconway@rogers.com>
PGP Key ID: DB3C29FC