Try connecting to both postgres and template1 databases to do the initial

Try connecting to both postgres and template1 databases to do the initial
inspection of shared catalogs.  This allows pg_dumpall to continue to
work with pre-8.1 servers that likely won't have a database named postgres.
Also, suppress output of SYSID options for users and groups, since server
no longer does anything with these except emit a rude message.
There is much more to be done to update pg_dumpall for the roles feature,
but this at least makes it usable again.  Per gripe from Chris K-L.