pgsql: Avoid dangling pointer to relation name in RLS code path in DoCo

Avoid dangling pointer to relation name in RLS code path in DoCopy().

With RLS active, "COPY tab TO ..." failed under -DRELCACHE_FORCE_RELEASE,
and would sometimes fail without that, because it used the relation name
directly from the relcache as part of the parsetree it's building. That
becomes a potentially-dangling pointer as soon as the relcache entry is
closed, a bit further down. Typical symptom if the relcache entry chanced
to get cleared would be "relation does not exist" error with a garbage
relation name, or possibly a core dump; but if you were really truly
unlucky, the COPY might copy from the wrong table.

Per report from Andrew Dunstan that regression tests fail with
-DRELCACHE_FORCE_RELEASE. The core tests now pass for me (but have
not tried "make check-world" yet).

Discussion: /messages/by-id/7b52f900-0579-cda9-ae2e-de5da17090e6@2ndQuadrant.com

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/a8df75b0a470f477dad75a7408e429e10c13fc07

Modified Files
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src/backend/commands/copy.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

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