pgsql: Prevent a rowtype from being included in itself via a range.

Prevent a rowtype from being included in itself via a range.

We probably should have thought of this case when ranges were added,
but we didn't.  (It's not the fault of commit eb51af71f, because
ranges didn't exist then.)

It's an old bug, so back-patch to all supported branches.

Discussion: https://postgr.es/m/7782.1577051475@sss.pgh.pa.us

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/31dfa40a834177b8e989a59252ee3ce1a3309075

Modified Files
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src/backend/catalog/heap.c               | 9 +++++++++
src/test/regress/expected/rangetypes.out | 3 +++
src/test/regress/sql/rangetypes.sql      | 3 +++
3 files changed, 15 insertions(+)