setup.py should fail with a nice error message if two ArcGIS tools have the same name

[jjr8]

Currently, when a class's method is flagged as being exposed as an ArcGIS tool, CreateArcGISToolbox.exe creates a tool entry in the toolbox with the name ClassName.MethodName. It is unlikely, but possible, that two classes with the same name might each expose a method with the same name. I'm not sure what will happen in this case; probably CreateArcGISToolbox.exe will overwrite the first tool in the toolbox with the second one. In any case, setup.py should detect this situation and report a nice error message, asking the developer to rename one of the tools.