Updated selser to use information about (un)modified text nodes.

* Reverts some incorrect / hasty changes from previous commits.
  - prevNodeUnmodified, currNodeUnmodified flags should indeed be
    always updated in emitSepAndOutput because for text and comment
    nodes that are primarily separators, the content is buffered
    and we are interested in modification state for the most recent
    node for which there was output.

  - Comments are innocuous enough that there is no need to worry
    about selsering them. There is no potential for generating dirty
    diffs for them. So, eliminated diff-markers for comments in the
    DOMDiff algo.

* Added another spot which had a missing onSOL state update.

* Tweaked escapeText flag to only do it for modified text nodes or
  for text nodes found in sol position because indent-pre effects are
  not localized -- and block tags later in the line changes indent-pre
  behavior. So, if a block tag at the end of the line was deleted, the
  leading space will trigger an indent-pre unless escaped (even though
  the text node itself was unmodified).

* 20 tests had their blacklisted output changed.
  After a somewhat careful examination, I think the changes are all
  legitimate and in many cases, an improvement.

* 42 selser tests newly "failing".
  However, in all cases, the reports are false since selser is now more
  accurate (avoids nowiki in i/b scenarios and other scenarios based on
  information about unedited text nodes).

Change-Id: I6eb9a1062297e85dd157c0aaf1104a33f536a812
Merge "Updated selser to use information about (un)modified text nodes."