[multi-sources-removal] Drop entities.source column Since we remove federated multi-sources support, the same value ('system') is always stored in this column and so could be removed. Also, cleanup repository caches and a few api where the very same useless information could be removed. Closes #2919300, at last [jcr: restore sanity check of etype against schema in checkintegrity.has_eid]

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)