Add a rule to refuse `->` between 2 exported resources

[PierreR]

This is rather peculiar but I have just noticed that puppet (3.8.2) refuses -> between two exported resources.

If it is indeed intended (not a puppet bug), we might want to add a rule to refuse such syntax:

  @@postgresql::server::pg_hba_rule { 'pg_hba open local access for salt':
    description => 'MD5 access to the puppetdb database',
    type        => 'local',
    database    => $db_name,
    user        => $db_user,
    auth_method => 'trust',
  } ->
  @@postgresql_psql {'create table jids':
    db          => $db_name,
   ......

[bartavelle]

Can you try the following cases too ?

@@foo -> bar
foo -> @@bar