[#636769] Fix for major rexec bugs
* Lib/rexec.py
(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.
* Lib/ihooks.py
(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.
* Misc/NEWS
Document the change.
ihooks.ModuleLoader does not implement reload(mod) correctly:
If mod has already been loaded by ModuleLoader, it has
been returned from a cache. Added an additional parameter
to import_it() to force reloading.