[application/connect] simplify connection logic ``application.connect`` now either sets a full featured ``DBAPISession`` to the ``WebRequest`` object or raises ``AuthenticationError``. The creation and usage of a fake DBAPISession is now handled by ``main_handle_request`` when needed. This means that fake DBAPISession are no longer tracked by the session manager and that user are not given anyway to retrieve them for a later request. This fake DBAPISession is still passed to ``core_handle`` because multiple cubes like registration or forgotten password need this behavior. We would like to get ride of it in the future. This clarification of the connection API greatly simplifies ``DBAPISession`` retrieval//creation process opening the way to improvements in this area. Related to #2503918

try:
    rtype, = __args__
except ValueError:
    print 'USAGE: cubicweb-ctl shell <instance> detect_cycle.py -- <relation type>'
    print

graph = {}
for fromeid, toeid in rql('Any X,Y WHERE X %s Y' % rtype):
    graph.setdefault(fromeid, []).append(toeid)

from logilab.common.graph import get_cycles

for cycle in get_cycles(graph):
    print 'cycle', '->'.join(str(n) for n in cycle)