message: Fix verify_checks_output.
  This was accidentally broken in
  causing it to not check in the error case (which is the only case that mattered).
diff: @@ -737,7 +737,7 @@ impl Execs {
  }
  }
  - fn verify_checks_output(&self, output: &Output) {
  + fn verify_checks_output(&self, stdout: &[u8], stderr: &[u8]) {
  if self.expect_exit_code.unwrap_or(0) != 0
  && self.expect_stdout.is_none()
  && self.expect_stdin.is_none()
  @@ -758,8 +758,8 @@ impl Execs {
  "`with_status()` is used, but no output is checked.\n\
  The test must check the output to ensure the correct error is triggered.\n\
  --- stdout\n{}\n--- stderr\n{}",
  - String::from_utf8_lossy(&output.stdout),
  - String::from_utf8_lossy(&output.stderr),
  + String::from_utf8_lossy(stdout),
  + String::from_utf8_lossy(stderr),
  );
  }
  }
  @@ -806,13 +806,13 @@ impl Execs {
  }
  fn match_output(&self, actual: &Output) -> Result<()> {
  - self.verify_checks_output(actual);
  self.match_status(actual.status.code(), &actual.stdout, &actual.stderr)
  .and(self.match_stdout(&actual.stdout, &actual.stderr))
  .and(self.match_stderr(&actual.stdout, &actual.stderr))
  }
  fn match_status(&self, code: Option<i32>, stdout: &[u8], stderr: &[u8]) -> Result<()> {
  + self.verify_checks_output(stdout, stderr);
  match self.expect_exit_code {
  None => Ok(()),
  Some(expected) if code == Some(expected) => Ok(()),
  