Several bug fixes to extension parsing in tokenizer.

* Without regression testing for extensions in parserTests,
  these bugs are sneaking through and get caught during RT
  testing.

* en:List of Dallas Mavericks seasons displayed a regression in
  RT-testing which was a failure to correctly parse extension
  output when nested in a template. This bug slipped through
  because I moved around code in the tokenizer incorrectly.

  In the bargain, I found 2 other bugs (3 for the price of 1)
  which mostly cancelled each other out (horror of horrors!)

  1. It appears that to fail a production, I ought to return null
     rather than false.
  2. But I was not matching the right #* length in a production
     which would have failed normally except I returned false
     instead of null as in 1. :)

* Also discovered that natively supported extensions (ref) were
  not getting parsed properly after commit d8643a11.

* Fixes the rt regression on en:List of Dallas Mavericks

* No change in parser test results.

Change-Id: Ide730c5a56d3442b0fd6e26e03d325b7a419bf25