vfs: ensure closewrapbase fh doesn't escape by entering context manager I'm not sure if there's a problem in practice here, as there's no test failure either way. The __exit__() and close() methods raise an exception, so maybe __exit__() and close() are being called directly on the underlying handle when delayclosedfile is used on a context manager? I doubt that was intended.

windows: ensure mixedfilemodewrapper fd doesn't escape by entering context mgr Otherwise it seems that the special read and write handling would be bypassed.

py3: ensure the proxied Windows fd doesn't escape by entering context manager The purpose of the proxy class is to provide the `name` attribute which contains the file path. But in tests that used a context manager, it still blew up complaining that 'int' doesn't have a 'startswith' function.