copied more places than I first thought it would. This fixes a bug:
a couple of these places were neglecting to enforce USAGE access on
explicitly-referenced schemas.
documentation (xindex.sgml should be rewritten), need to teach pg_dump
about it, need to update contrib modules that currently build pg_opclass
entries by hand. Original patch by Bill Studenmund, grammar adjustments
and general update for 7.3 by Tom Lane.