pgsql: Add support for systemd service notifications

Add support for systemd service notifications

Insert sd_notify() calls at server start and stop for integration with
systemd.  This allows the use of systemd service units of type "notify",
which greatly simplifies the systemd configuration.

Reviewed-by: Pavel Stěhule <pavel.stehule@gmail.com>

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/7d17e683fcc28a1b371c7dd02935728cd2cbf9bf

Modified Files
--------------
configure                           | 49 +++++++++++++++++++++++++++++++++++++
configure.in                        | 13 ++++++++++
doc/src/sgml/installation.sgml      | 16 ++++++++++++
doc/src/sgml/runtime.sgml           | 35 ++++++++++++++++++++++++++
src/Makefile.global.in              |  1 +
src/backend/Makefile                |  4 +++
src/backend/postmaster/postmaster.c | 26 ++++++++++++++++++++
src/include/pg_config.h.in          |  3 +++
8 files changed, 147 insertions(+)