FSS Renderer shouldn't shorten IRIs to PNAME_NS's

OWL FSS does not allow abbreviated IRIs to be precisely equal to a namespace prefix - 
for example, this is invalid: ```NamedIndividual(rdf:)``` ; however  ```NamedIndividual(rdf:type)``` is fine.

Turtle (and SPARQL) do allow PNAME_NS as IRIs:
```
rdf:  rdf:type owl:NamedIndividual . 
rdf:type  rdf:type owl:NamedIndividual . 
``` 
is quite alright.

This pull request fixes this issue #213 .