bitmap in wx3.0 doesn't have useAlpha() method

Suppress WXDEBUG assertions, as happens by default with wx2.8. This is
necessary for wx3.0

Exception while connecting LOCAL://!
Traceback (most recent call last):
File "/home/beremiz/beremiz/ProjectController.py", line 1560, in _Connect
self._SetConnector(connectors.ConnectorFactory(uri, self))
File "/home/beremiz/beremiz/ProjectController.py", line 1508, in _SetConnector
self.StatusTimer.Start(milliseconds=500, oneShot=False)
File "/usr/lib/python2.7/dist-packages/wx-3.0-gtk2/wx/_misc.py", line 1324, in Start
return _misc_.Timer_Start(*args, **kwargs)
PyAssertionError: C++ assertion "m_window" failed at ../src/gtk/dcclient.cpp(2043) in DoGetSize(): GetSize() doesn't work without window

enable use of wxWidgets-3.0