libctf: fix ctf_type_pointer on parent dicts, etc

libctf: fix ctf_type_pointer on parent dicts, etc

Before now, ctf_type_pointer was crippled: it returned some type (if any)
that was a pointer to the type passed in, but only if both types were in the
current dict: if either (or both) was in the parent dict, it said there was
no pointer though there was.  This breaks real users: it's past time to lift
the restriction.

WIP (complete, but not yet tested).