pgsql: Add support for an application_name parameter, which is displayed

Log Message:
-----------
Add support for an application_name parameter, which is displayed in
pg_stat_activity and recorded in log entries.

Dave Page, reviewed by Andres Freund

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.234 -> r1.235)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.234&r2=1.235)
        libpq.sgml (r1.289 -> r1.290)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml?r1=1.289&r2=1.290)
        monitoring.sgml (r1.71 -> r1.72)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/monitoring.sgml?r1=1.71&r2=1.72)
    pgsql/src/backend/catalog:
        system_views.sql (r1.61 -> r1.62)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/catalog/system_views.sql?r1=1.61&r2=1.62)
    pgsql/src/backend/postmaster:
        pgstat.c (r1.192 -> r1.193)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/pgstat.c?r1=1.192&r2=1.193)
    pgsql/src/backend/utils/adt:
        pgstatfuncs.c (r1.54 -> r1.55)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/pgstatfuncs.c?r1=1.54&r2=1.55)
    pgsql/src/backend/utils/error:
        elog.c (r1.218 -> r1.219)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c?r1=1.218&r2=1.219)
    pgsql/src/backend/utils/misc:
        guc.c (r1.523 -> r1.524)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.523&r2=1.524)
        postgresql.conf.sample (r1.269 -> r1.270)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.269&r2=1.270)
    pgsql/src/include/catalog:
        catversion.h (r1.551 -> r1.552)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h?r1=1.551&r2=1.552)
        pg_proc.h (r1.552 -> r1.553)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.552&r2=1.553)
    pgsql/src/include:
        pgstat.h (r1.83 -> r1.84)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/pgstat.h?r1=1.83&r2=1.84)
    pgsql/src/include/utils:
        guc.h (r1.108 -> r1.109)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc.h?r1=1.108&r2=1.109)
    pgsql/src/interfaces/libpq:
        fe-connect.c (r1.377 -> r1.378)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c?r1=1.377&r2=1.378)
        libpq-int.h (r1.144 -> r1.145)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h?r1=1.144&r2=1.145)
    pgsql/src/test/regress/expected:
        rules.out (r1.151 -> r1.152)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/rules.out?r1=1.151&r2=1.152)