pgsql: Fix two ancient memory-leak bugs in relcache.c.

Fix two ancient memory-leak bugs in relcache.c.

RelationCacheInsert() ignored the possibility that hash_search(HASH_ENTER)
might find a hashtable entry already present for the same OID. However,
that can in fact occur during recursive relcache load scenarios. When it
did happen, we overwrote the pointer to the pre-existing Relation, causing
a session-lifespan leakage of that entire structure. As far as is known,
the pre-existing Relation would always have reference count zero by the
time we arrive back at the outer insertion, so add code that deletes the
pre-existing Relation if so. If by some chance its refcount is positive,
elog a WARNING and allow the pre-existing Relation to be leaked as before.

Also, AttrDefaultFetch() was sloppy about leaking the cstring form of the
pg_attrdef.adbin value it's copying into the relcache structure. This is
only a query-lifespan leakage, and normally not very significant, but it
adds up during CLOBBER_CACHE testing.

These bugs are of very ancient vintage, but I'll refrain from back-patching
since there's no evidence that these leaks amount to anything in ordinary
usage.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/078b2ed291c758e7125d72c3a235f128d40a232b

Modified Files
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src/backend/utils/cache/relcache.c | 69 +++++++++++++++++++++++++-----------
1 file changed, 48 insertions(+), 21 deletions(-)