Ignore more build products
Fall back onto PySide if availible
Check for PySide first, and proxy PyQt4 to it

This allows our other tools, which are rather dumb,
to import the wrong one and generally continue to
work.
Even out {sip,shiboken}.wrapinstance differences
Even out QtCore.{pyqtSignal.Signal} differences

This is, perhaps, going too far.
Typo