Handle text nodes that follow a token that ends a line.

* "=h=\na <div>foo</div>" parses into HTML where the h1-tag
  is followed by "\na " text node that is not wrapped in an
  element tag.  This was not being handled properly since
  the leading newline in the text node would lead to a
  duplicate newline if both newlines are emitted.

* Added a special case for text-nodes that handles this case.

  - Once we do another round of refactoring of all handlers
    to separate startsLine/endsLine in some fashion so that
    emitSeparator has access to them, we can handle this
	there by relying on surrounding DOM context.
  - That refactoring is waiting till we deal with all major
    regressions in white-space serialization.

* Fixes RTing of:
  "=h\na <div>foo</div>" as well as
  "=h    \na <div>foo</div>"

* No change in parser tests (TODO: add new tests)

* Eliminates RT errors from en:Aleksey Tolstoy

Change-Id: I25372b7093578f510a788422164a32e3e1845c25