Change the module registration declarations and change the object creation and

Change the module registration declarations and change the object creation and
deallocation to match those in the Python/C tutorial.  This has been done to
make the interface here more conventional, in the hunt for bug #411.  One
double deallocation has been fixed, but this would only occur if we failed to
create the connection to Xenstore, and so unfortunately is not the cause of
that bug.

Signed-off-by: Ewan Mellor <ewan@xensource.com>