pgsql: Repair incorrect check for coercion of unknown literal to

Log Message:
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Repair incorrect check for coercion of unknown literal to ANYARRAY, a bug
I introduced in 7.4.1 :-(. It's correct to allow unknown to be coerced to
ANY or ANYELEMENT, since it's a real-enough data type, but it most certainly
isn't an array datatype. This can cause a backend crash but AFAICT is not
exploitable as a security hole. Per report from Michael Fuhr.

Note: as fixed in HEAD, this changes a constant in the pg_stats view,
resulting in a change in the expected regression outputs. The back-branch
patches have been hacked to avoid that, so that pre-existing installations
won't start failing their regression tests.

Tags:
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REL8_0_STABLE

Modified Files:
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pgsql/src/backend/parser:
parse_coerce.c (r2.126.4.2 -> r2.126.4.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_coerce.c.diff?r1=2.126.4.2&r2=2.126.4.3)