pgsql: Include NOLOGIN roles in the 'flat' password file.

Log Message:
-----------
Include NOLOGIN roles in the 'flat' password file.  In the original
coding this was seen as useless, but the problem with not including them
is that the error message will often be something about authentication
failure, rather than the more helpful one about 'role is not permitted
to log in'.  Per discussion.

Modified Files:
--------------
    pgsql/src/backend/utils/init:
        flatfiles.c (r1.27 -> r1.28)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/init/flatfiles.c?r1=1.27&r2=1.28)