tests: allow xrange warning from perf.py...
tests: allow xrange warning from perf.py
The use of xrange in this file is acceptable.
We need to make the output optional - and not conditional on
the Python version - because `pyflakes` could be executed by any
Python version and pyflakes behaves differently depending on the
Python version.
Differential Revision:
https://phab.mercurial-scm.org/D6990