callMethod(o, attr, ...) is just a special case of:
call(getattr(o, attr), ...)
Starting with import version 1.4, call() now accepts a
Python callable as alternative to the function name.
The converter shouldn't need to deal with PyObject * itself, but use
only PyObjectRef, which takes care of reference already.
Make the GIL state management easier to read.
Add a small test that shows how to pass Python objects to/from QML.
