pgsql: Sort the dependent objects before deletion in DROP OWNED BY.

Sort the dependent objects before deletion in DROP OWNED BY.

This finishes a task we left undone in commit f1ad067fc, by extending
the delete-in-descending-OID-order rule to deletions triggered by
DROP OWNED BY.  We've coped with machine-dependent deletion orders
one time too many, and the new issues caused by Peter G's recent
nbtree hacking seem like the last straw.

Discussion: https://postgr.es/m/E1h6eep-0001Mw-Vd@gemulon.postgresql.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8aa9dd74b36757342b6208fbfebb5b35c2d67c53

Modified Files
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src/backend/catalog/dependency.c  | 17 +++++++++++++++++
src/backend/catalog/pg_shdepend.c |  8 ++++++++
src/include/catalog/dependency.h  |  2 ++
3 files changed, 27 insertions(+)