(FileBase): Added 'xreadlines' and '__iter__' to allowed file methods.
(FileWrapper.__init__): Removed unnecessary self.f variable, which gave
direct access to the file object.
(RExec): Added 'xreadlines' and '_weakref' to allowed modules.
(RExec.r_open): Convert string subclasses to a real string classes
before doing comparisons with mode parameter.
(BasicModuleImporter.import_module/reload/unload): Convert the module
name to a real string before working with it.
(ModuleImporter.import_module/import_it/reload): Convert the module
name to a real strings before working with it.