Temp fix for SMW\Test\QueryPrinterRegistryTestCase

Due to changes as to when test classes are loaded, some third-party
extension make assumptions about available test cases.

Removed SemanticMediaWikiTestCase dependency and solely
depend on \PHPUnit_Framework_TestCase

Only glanced over some of those tests but they need some serious re-factoring.
Merge pull request #310 from SemanticMediaWiki/fix-queryprinter-test-autoload

Temp fix for SMW\Test\QueryPrinterRegistryTestCase