Fix SEGV on exit after domainEventDeregister()
Fix SEGV on exit after domainEventDeregister()

When the last callback is removed using domainEventDeregister(), the
events dispatcher is deregistered from the C-library, but
domainEventsCallbacks is still an empty list.
On shutdown __del__() deregisters the dispatacher again, which SEGVs

	# You need the event-loop implementation from the Python examples;
	# give the file a name which is importable by Python.
	ln examples/domain-events/events-python/event-test.py eloop.py
	python -c 'from eloop import *
	import sys

	def dump(*args): print " ".join(map(str, args))

	virEventLoopPureStart()
	c = libvirt.open("xen:///")
	c.domainEventRegister(dump, None)
	c.domainEventDeregister(dump)
	sys.exit(0)'

domainEventDeregister() needs to delete domainEventCallbacks so subsequent
calls to __del__() and domainEventRegister() choose the right code paths.
Setting it to None is not enough, since calling domainEventRegiser() again
would trigger an TypeError.

Signed-off-by: Philipp Hahn <8cb7a2c205789112a9f61bc3102305826b6a8db1@univention.de>

cardoe/libvirt-python,libvirt/libvirt-python,cardoe/libvirt-python,libvirt/libvirt-python,libvirt/libvirt-python,cardoe/libvirt-python