pgsql: Test code for shared memory message queue facility.

Test code for shared memory message queue facility.

This code is intended as a demonstration of how the dynamic shared
memory and dynamic background worker facilities can be used to establish
a group of coooperating processes which can coordinate their activities
using the shared memory message queue facility.  By itself, the code
does nothing particularly interesting: it simply allows messages to
be passed through a loop of workers and back to the original process.
But it's a useful unit test, in addition to its demonstration value.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/4db3744f1f43554b03d8193da4645a0a5326eb18

Modified Files
--------------
contrib/Makefile                             |    1 +
contrib/test_shm_mq/.gitignore               |    4 +
contrib/test_shm_mq/Makefile                 |   20 ++
contrib/test_shm_mq/expected/test_shm_mq.out |   18 ++
contrib/test_shm_mq/setup.c                  |  323 ++++++++++++++++++++++++++
contrib/test_shm_mq/sql/test_shm_mq.sql      |    9 +
contrib/test_shm_mq/test.c                   |  265 +++++++++++++++++++++
contrib/test_shm_mq/test_shm_mq--1.0.sql     |   19 ++
contrib/test_shm_mq/test_shm_mq.control      |    4 +
contrib/test_shm_mq/test_shm_mq.h            |   45 ++++
contrib/test_shm_mq/worker.c                 |  224 ++++++++++++++++++
11 files changed, 932 insertions(+)