(PUP-1597) Fix contain functions lookup of class with leading ::

When the contain function creates edges it looked up resources
without removing the leading :: in the name. The catalog never stores
these, and thus an edge was formed between a resource and nil.

This commit simply removes the ::. There is no checking that a resource
is actually returned since they should all be there due to the call to
include them in the catalog (which would fail if it was not possible to
include them).

A test is also added for the erronous (and now fixed case).