SES-1718 : Removed duplicate results from Explore page when context URI is also in graph.

* Wrote a suite of regression tests that were made to pass.
* Also snuck in a minor PMD warning fix on TupleServlet.
Merged in dvisser/sesame/ses-1718 (pull request #55)

SES-1718 : Removed duplicate results from Explore page when context URI is also in graph.