fix for issue1429

[ghost]

Fixes #1429

Proposed Changes

• add an internal iri-to-uri conversion utility

why park this in the "restore-pyrdfa" branch? This fix will work for non-HTML sources with non-ASCII chars in the IRI, perhaps something like http://example.com/thing/Almería.ttl for instance. So this is a generic fix for parse()

I was both unclear and pedantic - I meant that the specific dbpedia example URL provided (which actually pointed to a text/html resource) is parsed without issue with the implementation coded therein and pyRfda enabled.

Providing a generic fix for parse() proved (as ever, with RDFLib) more tricky ....

Tactics:

1. The encoding of query param content "=" as "%3D" causes the failure of
   GraphTestCase::testGuessFormatForParse in that
   https://linked.data.gov.au/def/agrif?_format=text/turtle
   is converted to:
   https://linked.data.gov.au/def/agrif?_format%3dtext/turtle
   which returns a resource of text/html mimetype, triggering a "no plugin found" Exception.
   So, either decode the encoded "%3D" and friends or skip the conversion of query params altogether - I chose the former.

2. urllib omits the empty fragment identifier and the reassembled uri is stripped of any trailing "#" that the iri might have had, which causes the failure of
   NamedGraphWithFragmentTest::test_named_graph_with_fragment
   so it has to be explicitly restored to the end of the uri.

[ghost]

And, of course, Windows blows up:
OSError: [Errno 22] Invalid argument: '\\D:\\a\\rdflib\\rdflib\\test\\DAWG\\data-r2\\manifest-evaluation.ttl'

I'll need to check this out on a Windows VM.

[ghost]

Broken PR, consign to git hell.