Added a test case simulating hangs during shutdown with IPR render.
Updated bindings to match changes to IECore::RefCountedClass.

Fixes #855, through the GILReleasePtr introduced in the corresponding Cortex changes.
Merge pull request #892 from johnhaddon/iprShutdownFix

IPR shutdown deadlock fix
Updated default build to use PySide 1.2.2.