Simpler + more accurate inter-elt ws-&-comment-run detection.

* Replaced complex conditional checking based ws-and-comment-run
  detection with fsm-style detection.  The old code was also a
  little buggy and didn't detect these runs in all scenarios.

* Unlike old code that removed these nodes without leaving a trace
  the new code replaces the run with a meta node that records the
  separator source.  This will be useful when DSR is unavailable,
  for example, in the face of edit changes in the VE.  The current
  patch does not yet make use of the meta, but will in future
  patches.

* Also, minor cleanup of emitSeparator to use symbolic names for
  separator type.

* No change in parser test results.

* Fixes RT regressions on this page (and possibly other pages).
  en/Wikipedia:Articles for deletion/Log/2008 October 16

Change-Id: Ic1032f0aff5add8fbad25468bc6db55303a11269