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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REL9_4_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0d245d13c643d9ee089ad59fc4673a6b520461b1

Modified Files
--------------
src/backend/catalog/heap.c               |  9 +++++++++
src/test/regress/expected/rangetypes.out | 19 +++++++++++++++++++
src/test/regress/sql/rangetypes.sql      | 16 ++++++++++++++++
3 files changed, 44 insertions(+)