pgsql: Limit depth of forced recursion for CLOBBER_CACHE_RECURSIVELY.

Limit depth of forced recursion for CLOBBER_CACHE_RECURSIVELY.

It's somewhat surprising that we got away with this before.  (Actually,
since nobody tests this routinely AFAIK, it might've been broken for
awhile.  But it's definitely broken in the wake of commit f868a8143.)
It seems sufficient to limit the forced recursion to a small number
of levels.

Back-patch to all supported branches, like the preceding patch.

Discussion: https://postgr.es/m/12259.1532117714@sss.pgh.pa.us

Branch
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REL9_3_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/f112d4088c29997bd777a8934b11a797132391db

Modified Files
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src/backend/utils/cache/inval.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)