[IR] Deleted pre-1.9 semantics for non-local returns.

* Non-local returns always throw LocalJumpError for bad returns
  whereas in 1.8 return from thread would throw a ThreadError.
  This commit removes the 1.8 semantics which leads to one more
  spec passing.

* Added additional protection in non-local return handling for
  null scopeTypes (to be investigated) in thread bodies. This
  leads to one more spec passing.

* Now down to 7 failures + 2 errors.