Revert "Overriding __redirect_uri method in GitHubAccount"

This reverts commit 288ff4789f976114fd1133b2ca0e99744fbaec2f.

That would have been an elegant fix, with no patches to web2py required. But it won't work due to Python's name manging on methods that start with double underscore:

http://docs.python.org/2/tutorial/classes.html#private-variables-and-class-local-references
More annoying fix for failing OAuth logins