tests/test-check-pyflakes.t

tests: restore Python 3 compat in test-parseindex2.py

I think this was previously getting lucky in Python 3, and would have
stacktraced if something failed. Now that failure messages are eagerly
computed, this turned into a problem.

Differential Revision: https://phab.mercurial-scm.org/D4182

#require test-repo pyflakes hg10

  $ . "$TESTDIR/helpers-testrepo.sh"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ cat > test.py <<EOF
  > print(undefinedname)
  > EOF
  $ pyflakes test.py 2>/dev/null | "$TESTDIR/filterpyflakes.py"
  test.py:1: undefined name 'undefinedname'
  
  $ cd "`dirname "$TESTDIR"`"

  $ testrepohg locate 'set:**.py or grep("^#!.*python")' \
  > -X hgext/fsmonitor/pywatchman \
  > -X mercurial/pycompat.py -X contrib/python-zstandard \
  > -X mercurial/thirdparty/cbor \
  > -X mercurial/thirdparty/concurrent \
  > -X mercurial/thirdparty/zope \
  > 2>/dev/null \
  > | xargs pyflakes 2>/dev/null | "$TESTDIR/filterpyflakes.py"