Fix test that checks if a DOM node is original or new content

* The existing test was looking at the presence / absence of
  the data-parsoid attribute. However, once we stripped data-parsoid
  from template content in 320caa30, the original test was
  no longer sufficient.

  This caused false roundtrip diffs in roundtrip-testing.

  Try "node roundtrip-test.js --prefix kowiki 민아"
  vs. looking at http://localhost:8000/_rt/kowiki/민아

  The former runs in roundtrip-test mode (no-edits) and the
  latter runs in edit mode.

  In roundtrip-test mode, a mw:Placeholder/StrippedTag meta
  without a data-parsoid attribute was changing the newline
  constraints since the meta was being treated as new content
  without the data-parsoid attribute.

* While we should fix the newline constraints code separately
  to look at the meta typeof, this patch fixes the isNewElt
  fix to be more robust -- it now tests the newness of the
  first top-level node of templated/extension content (which
  doesn't gets its data-parsoid stripped).

* This fixes the roundtrip-test.js output on the kowiki page
  above.

Change-Id: Ibaf3f544f34d16b3f8ae76bc1b2a4e563e438988
Merge "Fix test that checks if a DOM node is original or new content"