tests/test-check-jshint.t

windows: always work around EINVAL in case of broken pipe for stdout / stderr

In 29a905fe23ae, I missed the fact that the `winstdout` class works around two
unrelated bugs (size limit when writing to consoles and EINVAL in case of
broken pipe) and that the latter bug happens even when no console is involved.
When writing a test for this, I realized that the same problem applies to
stderr, so I applied the workaround for EINVAL to both stdout and stderr.

The size limit is worked around in the same case as before (consoles on Windows
on Python 2). For that, I changed the `winstdout` class.

#require test-repo jshint hg10

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

run jshint on all tracked files ending in .js except vendored dependencies

  $ cd "`dirname "$TESTDIR"`"

  $ testrepohg locate 'set:**.js' \
  > 2>/dev/null \
  > | xargs jshint