pgsql: Add PQping and PQpingParams to libpq to allow detection of the s

Add PQping and PQpingParams to libpq to allow detection of the server's
status, including a status where the server is running but refuses a
postgres connection.

Have pg_ctl use this new function. This fixes the case where pg_ctl
reports that the server is not running (cannot connect) but in fact it
is running.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=afd7d9adca971d9aae97e87ce617d8608d25ab10

Modified Files
--------------
doc/src/sgml/libpq.sgml | 68 +++++++++++++++++++++++++++++++++++++
src/bin/pg_ctl/pg_ctl.c | 29 +++++++---------
src/interfaces/libpq/exports.txt | 2 +
src/interfaces/libpq/fe-connect.c | 53 ++++++++++++++++++++++++++++
src/interfaces/libpq/libpq-fe.h | 10 +++++
5 files changed, 146 insertions(+), 16 deletions(-)