testsuite/pipeline.py (PipelineConstructor.testGoodConstructor) (PipelineConstructor.testBadConstruct)

Original commit message from CVS:
* testsuite/pipeline.py (PipelineConstructor.testGoodConstructor)
(PipelineConstructor.testBadConstruct)
(ThreadConstructor.testCreate): New tests

* testsuite/element.py (ElementTest.testGoodConstructor): Add
isinstance(element, gst.Element) test

* testsuite/common.py: Clean up, use ltihooks
(init) Assign tp_new for pipeline and thread to PyType_GenericNew
for now.