[COMMITTERS] pgsql: Again match pg_user_mappings toinformation_schema.user_mapping_

Again match pg_user_mappings to information_schema.user_mapping_options.

Commit 3eefc51053f250837c3115c12f8119d16881a2d7 claimed to make
pg_user_mappings enforce the qualifications user_mapping_options had
been enforcing, but its removal of a longstanding restriction left them
distinct when the current user is the subject of a mapping yet has no
server privileges.  user_mapping_options emits no rows for such a
mapping, but pg_user_mappings includes full umoptions.  Change
pg_user_mappings to show null for umoptions.  Back-patch to 9.2, like
the above commit.

Reviewed by Tom Lane.  Reported by Jeff Janes.

Security: CVE-2017-7547

Branch
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REL9_4_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b6e39ca92eeee4e5fa0e83ce3e04dad82559983f

Modified Files
--------------
doc/src/sgml/catalogs.sgml                 | 32 ++++++++++++++++++++++++------
src/backend/catalog/system_views.sql       |  4 +++-
src/test/regress/expected/foreign_data.out | 32 ++++++++++++++++--------------
src/test/regress/expected/rules.out        |  2 +-
src/test/regress/sql/foreign_data.sql      | 17 +++++++++-------
5 files changed, 57 insertions(+), 30 deletions(-)