[sage-devel] Example graphs and show()

[Jori Mäntysalo]

Many examples at graph_generators.py use show() as an example of use. What 
you think about this? It tests that plotting of the graph does not return 
an error, but nothing more. And it will take time, not that much but 
cutting the testing time would not be a bad idea.

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Jori Mäntysalo