pgsql: Switch user ID to the object owner when populating a materialize

Switch user ID to the object owner when populating a materialized view.

This makes superuser-issued REFRESH MATERIALIZED VIEW safe regardless of
the object's provenance.  REINDEX is an earlier example of this pattern.
As a downside, functions called from materialized views must tolerate
running in a security-restricted operation.  CREATE MATERIALIZED VIEW
need not change user ID.  Nonetheless, avoid creation of materialized
views that will invariably fail REFRESH by making it, too, start a
security-restricted operation.

Back-patch to 9.3 so materialized views have this from the beginning.

Reviewed by Kevin Grittner.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/f3ab5d46960023cf8a9df3751ab9748ce01a46a0

Modified Files
--------------
doc/src/sgml/ref/create_materialized_view.sgml |    4 +++-
src/backend/commands/createas.c                |   30 ++++++++++++++++++++++++
src/backend/commands/matview.c                 |   19 +++++++++++++++
3 files changed, 52 insertions(+), 1 deletion(-)