'Checks whether there are circular dependency conflicts.
>>> tracker = DependencyTracker()
>>> tracker.add(0, 1)
>>> tracker.add(1, 0)
>>> tracker.check_circular_dependencies()
Traceback (most recent call last):
coalib.core.CircularDependencyError.CircularDependencyError: ...
:raises CircularDependencyError:
Raised on circular dependency conflicts.'

def check_circular_dependencies(self):

    traverse_graph(self._dependency_dict.keys(), (lambda node: self._dependency_dict.get(node, frozenset())))
