util: cast memoryview to bytes Python 3 uses readinto() instead of read() in places. And taking a slice of the buffer passed to readinto() will produce a memoryview. _writedata() then gets confused when testing for `b'\n' in data` because memoryview is an iterable over ints instead of 1 character bytes. We work around by casting a memoryview to bytes. Differential Revision: https://phab.mercurial-scm.org/D5704