pgsql: Add pg_sequences view

Add pg_sequences view

Like pg_tables, pg_views, and others, this view contains information
about sequences in a way that is independent of the system catalog
layout but more comprehensive than the information schema.

To help implement the view, add a new internal function
pg_sequence_last_value() to return the last value of a sequence.  This
is kept separate from pg_sequence_parameters() to separate querying
run-time state from catalog-like information.

Reviewed-by: Andreas Karlsson <andreas@proxel.se>

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/67dc4ccbb2e1c27da823eced66d9217a5652cbb0

Modified Files
--------------
doc/src/sgml/catalogs.sgml               | 97 ++++++++++++++++++++++++++++++++
src/backend/catalog/system_views.sql     | 17 ++++++
src/backend/commands/sequence.c          | 49 +++++++++++++++-
src/include/catalog/catversion.h         |  2 +-
src/include/catalog/pg_proc.h            |  4 +-
src/include/commands/sequence.h          |  1 +
src/test/regress/expected/rules.out      | 14 +++++
src/test/regress/expected/sequence.out   | 23 +++++++-
src/test/regress/expected/sequence_1.out | 23 +++++++-
src/test/regress/sql/sequence.sql        | 13 ++++-
10 files changed, 233 insertions(+), 10 deletions(-)