pgsql: Add GUC variables to control keep-alive times for idle, interval,

Log Message:
-----------
Add GUC variables to control keep-alive times for idle, interval, and
count.

Oliver Jowett

Modified Files:
--------------
    pgsql/doc/src/sgml:
        runtime.sgml (r1.339 -> r1.340)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/runtime.sgml.diff?r1=1.339&r2=1.340)
    pgsql/src/backend/libpq:
        pqcomm.c (r1.176 -> r1.177)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/pqcomm.c.diff?r1=1.176&r2=1.177)
    pgsql/src/backend/utils/misc:
        guc.c (r1.279 -> r1.280)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.279&r2=1.280)
        postgresql.conf.sample (r1.154 -> r1.155)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample.diff?r1=1.154&r2=1.155)
    pgsql/src/bin/psql:
        tab-complete.c (r1.135 -> r1.136)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/tab-complete.c.diff?r1=1.135&r2=1.136)
    pgsql/src/include/libpq:
        libpq-be.h (r1.49 -> r1.50)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/libpq/libpq-be.h.diff?r1=1.49&r2=1.50)
    pgsql/src/include/utils:
        guc.h (r1.61 -> r1.62)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc.h.diff?r1=1.61&r2=1.62)