thanks for spotting this. although the rdf extension does import `URIRef`, i think we can clean this function. however, when one runs this function with `URIRef` without this check, it returns unicode.

```
In [2]: from rdflib import URIRef
In [3]: uri = URIRef('http://example.com/')

In [4]: _auto_literal_conversion(uri)
Out[4]: u'http://example.com/'

In [8]: _auto_literal_conversion2(uri)
Out[8]: rdflib.term.URIRef(u'http://example.com/')
```

and that's because:

```
In [3]: isinstance(uri, basestring)
Out[3]: True
```