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_4_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/35e39610a3f83e0464cb2ff2b1e4c282d323b602

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