tests/unwrap-message-id.py

tests: consistently use pyflakes as a Python module

We check availability of pyflakes as a module, and also running it for real as
a module. Only fair to test filterpyflakes.py working correctly when using
pyflakes as a module too.

This is a graft of a similar fix that ended up on default.

Differential Revision: https://phab.mercurial-scm.org/D8629

from __future__ import absolute_import, print_function

import sys

for line in sys.stdin:
    if line.lower() in ("message-id: \n", "in-reply-to: \n"):
        line = line[:-2]
    print(line, end="")