[repository] when deleting relations of a deleted external entity, we should skip non-crossable relation (closes #1973680) elses this may lead to things as described in the ticket...

from os.path import join
from cubicweb.toolsutils import create_dir

option_renamed('pyro-application-id', 'pyro-instance-id')

create_dir(join(config.appdatahome, 'backup'))