Kludge for #5048 -- serialization compatibility with 0.25.x

In 0.25.x the type & title of a resource were wrapped in a Puppet::Resource::Reference
object whereas in 2.6.x they are attributes of the resource itself without the
additional indirection (see 7089446697ad550c22012bc2b5572030727d67e1).

When pson serialization is used this isn’t a problem but with formats in which
we just blindly emit the structure either because we have no choice (marshal)
or because we just use the default (yaml) it is a compatibility-breaking change.

This patch resoloves the problem by adding a dummy reference object to cause
the "correct" serialization; it is intended as a stop-gap for 2.6.x and should
NOT be merged into next.