tests/test-check-pyflakes.t

tests: on windows, run command explicitly in sh for working command substitution

On windows, os.system runs the command in cmd.exe, which does not know command
substitution. To let this work, run the command explicitly in sh.

This fixes the failure of this test on windows.

  $ "$TESTDIR/hghave" pyflakes || exit 80
  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)
  $ hg manifest 2>/dev/null | egrep "\.py$|^[^.]*$" | grep -v /random_seed$ \
  > | xargs pyflakes 2>/dev/null | "$TESTDIR/filterpyflakes.py"
  contrib/win32/hgwebdir_wsgi.py:*: 'win32traceutil' imported but unused (glob)
  setup.py:*: 'sha' imported but unused (glob)
  setup.py:*: 'zlib' imported but unused (glob)
  setup.py:*: 'bz2' imported but unused (glob)
  setup.py:*: 'py2exe' imported but unused (glob)
  tests/hghave.py:*: 'hgext' imported but unused (glob)
  tests/hghave.py:*: '_lsprof' imported but unused (glob)
  tests/hghave.py:*: 'publish_cmdline' imported but unused (glob)
  tests/hghave.py:*: 'pygments' imported but unused (glob)
  tests/hghave.py:*: 'ssl' imported but unused (glob)
  contrib/win32/hgwebdir_wsgi.py:*: 'from isapi.install import *' used; unable to detect undefined names (glob)
  hgext/inotify/linux/__init__.py:*: 'from _inotify import *' used; unable to detect undefined names (glob)