Bug fix in HTML-pre TSR computation.

* pos value in the tokenizer is an absolute value, not an offset
  so endpos attribute on a <html-pre> token is not an offset.

  However, it needs to be offset wrt. the starting offset of the
  chunk because the tokenizer processes the input in chunks.
  This bit has always been a bit problematic because anyone who
  adds a new pos-type attribute to a token has to remember to
  update the code for Util.shiftTokenTSR

* Simplest test case to reproduce the buggy DSR inconsistency
  warning.
------
<p>
<pre>
foo
</pre></p>
------

* 11 fewer DSR inconsistency warnings as a result of this fix.

* 4 "additional" selser failures, but they are really improvements
  since the new selser output is more accurate compared to the
  non-selser WTS output.

Change-Id: Ide8309f73bfc347d7fb2b4eea08c199b96c3435e