pgsql: Code review for row security.

Code review for row security.

Buildfarm member tick identified an issue where the policies in the
relcache for a relation were were being replaced underneath a running
query, leading to segfaults while processing the policies to be added
to a query.  Similar to how TupleDesc RuleLocks are handled, add in a
equalRSDesc() function to check if the policies have actually changed
and, if not, swap back the rsdesc field (using the original instead of
the temporairly built one; the whole structure is swapped and then
specific fields swapped back).  This now passes a CLOBBER_CACHE_ALWAYS
for me and should resolve the buildfarm error.

In addition to addressing this, add a new chapter in Data Definition
under Privileges which explains row security and provides examples of
its usage, change \d to always list policies (even if row security is
disabled- but note that it is disabled, or enabled with no policies),
rework check_role_for_policy (it really didn't need the entire policy,
but it did need to be using has_privs_of_role()), and change the field
in pg_class to relrowsecurity from relhasrowsecurity, based on
Heikki's suggestion.  Also from Heikki, only issue SET ROW_SECURITY in
pg_restore when talking to a 9.5+ server, list Bypass RLS in \du, and
document --enable-row-security options for pg_dump and pg_restore.

Lastly, fix a number of minor whitespace and typo issues from Heikki,
Dimitri, add a missing #include, per Peter E, fix a few minor
variable-assigned-but-not-used and resource leak issues from Coverity
and add tab completion for role attribute bypassrls as well.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/6550b901fe7c47c03775400e0c790c6c1234a017

Modified Files
--------------
doc/src/sgml/catalogs.sgml           |   11 ++-
doc/src/sgml/config.sgml             |    4 +-
doc/src/sgml/ddl.sgml                |  168 ++++++++++++++++++++++++++++++++++
doc/src/sgml/ref/alter_table.sgml    |    2 +-
doc/src/sgml/ref/create_policy.sgml  |    2 +-
doc/src/sgml/ref/pg_dump.sgml        |   17 ++++
doc/src/sgml/ref/pg_restore.sgml     |   23 +++++
src/backend/catalog/heap.c           |    2 +-
src/backend/catalog/system_views.sql |    2 +-
src/backend/commands/policy.c        |   17 ++--
src/backend/commands/tablecmds.c     |    4 +-
src/backend/rewrite/rowsecurity.c    |   31 ++++---
src/backend/utils/adt/ri_triggers.c  |    4 +-
src/backend/utils/cache/relcache.c   |   91 +++++++++++++++++-
src/bin/pg_dump/pg_backup_archiver.c |   11 ++-
src/bin/pg_dump/pg_dump.c            |   36 ++++----
src/bin/pg_dump/pg_dump.h            |    2 +-
src/bin/pg_dump/pg_restore.c         |    2 +-
src/bin/psql/describe.c              |   79 +++++++++-------
src/bin/psql/tab-complete.c          |   38 ++++----
src/include/catalog/catversion.h     |    2 +-
src/include/catalog/pg_class.h       |    4 +-
src/include/commands/policy.h        |    7 +-
src/test/regress/expected/rules.out  |    2 +-
24 files changed, 439 insertions(+), 122 deletions(-)