I should add that the latest patches remove permissions checks because
pg_locks doesn't have any, and improve the commit messages. Hope I
didn't garble anything doing this late after the dev conference. :-)
Robert asked me about other existing functions that could be
leveraged, such as GetConflictingVirtualXIDs(), but I didn't see any
with close-enough semantics that handle fast-path locks as needed for
tables/relations.