find_cycle method does not work for digraph subclasses

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What steps will reproduce the problem?
1. Create a subclass of digraph: 
class X(digraph):
    # etc

2. Declare an instance, and attempt to call find_cycle:

instance = X()
cycles.find_cycle(instance)

This causes an InvalidGraphType exception to be thrown rather than the expected 
functionality (returning an empty list for the empty graph).

I am using the current version of python-graph-core, python 2.6 (installed 
using easy_install) on OS X 10.6.8.

Thanks,
Joshua T. Guerin (jtguer2@uky.edu)

Original issue reported on code.google.com by jtgue...@gmail.com on 20 Feb 2012 at 6:00

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Original comment by pmatiello on 20 Feb 2012 at 6:33

• Changed state: Accepted

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Thanks for your report. It's now fixed in r749.

Original comment by pmatiello on 20 Feb 2012 at 6:34

• Changed state: Fixed