pgsql: Fix subquery reference to non-populated MV in CMV.

Fix subquery reference to non-populated MV in CMV.

A subquery reference to a matview should be allowed by CREATE
MATERIALIZED VIEW WITH NO DATA, just like a direct reference is.

Per bug report from Laurent Sartran.

Backpatch to 9.3.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/b2cd72cbbdd2a1b657d7dc874fcc9f1c1d83d8e3

Modified Files
--------------
src/backend/executor/execMain.c       |    3 ++-
src/test/regress/expected/matview.out |    6 ++++++
src/test/regress/sql/matview.sql      |    6 ++++++
3 files changed, 14 insertions(+), 1 deletion(-)