Added missing check for pre when emitting separators.

* When emitting separator between last-child and parent,
  WTS was missing a check to see if the parent was a pre.
* Unrelated: improved tracing output of pre-handler a bit by
  emitting states as strings instead of numbers.
* Fixes RTing of snippet: "a<br/>\n \n b" which is a reduced
  test case from en:BAIRA
* No change in parser tests.  TODO: Add new ones.

Change-Id: I730b93497f7bc1189196acb664771ca80903dd30
Merge "Added missing check for pre when emitting separators."