pgsql: Split apart pg_upgrade user lookup and root check so '--help'

Log Message:
-----------
Split apart pg_upgrade user lookup and root check so '--help' shows
proper default username.

Modified Files:
--------------
pgsql/contrib/pg_upgrade:
option.c (r1.2 -> r1.3)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/pg_upgrade/option.c?r1=1.2&r2=1.3)