Fix ordering of postgres classes

The postgres lib devel class must not be included until after our
postgres primary class, as it inherits from postgresql::globals, and we
need to change the paramaters of this from within pp_postgres_server

This could be fixed by using a wrapper class that included both
pp_postgres::primary and postgresql::lib::devel and specified a resource
ordering, but there is no way to specify this without creating an extra
wrapper class.