pgsql: Accept 'on' and 'off' as input for boolean data type, unifying

Log Message:
-----------
Accept 'on' and 'off' as input for boolean data type, unifying the syntax
that the data type and GUC accepts.

ITAGAKI Takahiro

Modified Files:
--------------
    pgsql/doc/src/sgml:
        datatype.sgml (r1.235 -> r1.236)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datatype.sgml?r1=1.235&r2=1.236)
    pgsql/src/backend/utils/adt:
        bool.c (r1.45 -> r1.46)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/bool.c?r1=1.45&r2=1.46)
    pgsql/src/backend/utils/misc:
        guc.c (r1.496 -> r1.497)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.496&r2=1.497)
    pgsql/src/include/utils:
        builtins.h (r1.331 -> r1.332)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h?r1=1.331&r2=1.332)
        guc.h (r1.100 -> r1.101)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc.h?r1=1.100&r2=1.101)
    pgsql/src/test/regress/expected:
        boolean.out (r1.15 -> r1.16)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/boolean.out?r1=1.15&r2=1.16)
    pgsql/src/test/regress/sql:
        boolean.sql (r1.9 -> r1.10)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/boolean.sql?r1=1.9&r2=1.10)