py3: use pycompat.bytestr so that we don't get ascii values
This fixes `hg files 'set:(**.py)'` which makes test-check-py3-compat.t able to
run on Python 3. So if you now do `python3 ./run-tests.py
test-check-py3-compat`, the test will actually run.
local test passedaddgroupcopy test passedclone test passedlowlevelcopy test passed