Ian Moody <moz-ian@perix.co.uk> [Sat, 09 Mar 2019 00:44:26 +0000] rev 41955
py3: use pycompat.iterbytestr to convert memoryview slice to bytestring
Otherwise ch is the int value of the byte in py3 rather than the actual
character.
Differential Revision: https://phab.mercurial-scm.org/D6103