DegreeDistributionExport should output same format

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What steps will reproduce the problem?
1. Export DegreeDistribution with GUI
2. Export DegreeDistribution with CLI
3. If you run a diff between the generated files they don't match. This
is caused by different format for the probabilities (float/double).

What is the expected output? What do you see instead?
The probabilities format should be the same.

Please use labels and text to provide additional information.

You can check the ExportDegreeDistribution for Directed Graphs.
```

Original issue reported on code.google.com by `alvaro.andres.crespo@gmail.com` on 18 Dec 2013 at 9:21

Start by locating ExportDegreeDistribution for Directed Graphs, then trace the GUI and CLI export paths named in the report. Reproduce the export and compare the generated files, focusing on the probability formatting; done means both paths produce the same format and the resulting diff is empty.

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