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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REL7_4_STABLE

Modified Files:
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    pgsql/src/backend/parser:
        parse_coerce.c (r2.111.2.2 -> r2.111.2.3)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_coerce.c.diff?r1=2.111.2.2&r2=2.111.2.3)