[COMMITTERS] pgsql: Add CREATE COLLATION IF NOT EXISTS clause

Add CREATE COLLATION IF NOT EXISTS clause

The core of the functionality was already implemented when
pg_import_system_collations was added.  This just exposes it as an
option in the SQL command.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/6d16ecc646d21b39092970c591fd0f73b4cfc26b

Modified Files
--------------
doc/src/sgml/ref/create_collation.sgml           | 15 +++++++++++++--
src/backend/commands/collationcmds.c             |  4 ++--
src/backend/nodes/copyfuncs.c                    |  1 +
src/backend/nodes/equalfuncs.c                   |  1 +
src/backend/parser/gram.y                        | 20 ++++++++++++++++++++
src/backend/tcop/utility.c                       |  3 ++-
src/include/commands/collationcmds.h             |  2 +-
src/include/nodes/parsenodes.h                   |  1 +
src/test/regress/expected/collate.linux.utf8.out |  4 ++++
src/test/regress/sql/collate.linux.utf8.sql      |  2 ++
10 files changed, 47 insertions(+), 6 deletions(-)