py2swagger doesn't respect `http_method_names`

If a method (e.g. `patch`) is not contained in `http_method_names` of a View or a Viewset it will still appear in swagger.json

Start by locating the code that builds swagger.json for Views and Viewsets, then trace how http_method_names is read or ignored. Reproduce the case with a method such as patch excluded from http_method_names; done means that method no longer appears in the generated Swagger output.

Written by the indexing model from the issue text.