pgsql: Make log_min_error_statement put LOG level at the same priority

Log Message:
-----------
Make log_min_error_statement put LOG level at the same priority as
log_min_messages does; and arrange to suppress the duplicative output
that would otherwise result from log_statement and log_duration messages.
Bruce Momjian and Tom Lane.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        config.sgml (r1.112 -> r1.113)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.112&r2=1.113)
        sources.sgml (r2.27 -> r2.28)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/sources.sgml.diff?r1=2.27&r2=2.28)
    pgsql/src/backend/tcop:
        postgres.c (r1.525 -> r1.526)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c.diff?r1=1.525&r2=1.526)
    pgsql/src/backend/utils/error:
        elog.c (r1.182 -> r1.183)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c.diff?r1=1.182&r2=1.183)
    pgsql/src/backend/utils/misc:
        postgresql.conf.sample (r1.209 -> r1.210)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample.diff?r1=1.209&r2=1.210)
    pgsql/src/include/utils:
        elog.h (r1.83 -> r1.84)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/elog.h.diff?r1=1.83&r2=1.84)