This changes the behaviour of vectorize(disable). I.e., disabling vectorization
now means disabling vectorization, and not setting the vectorization width to 1.
This is a follow up of the discussion on the behaviour of different loop
pragmas, and that setting transformation options should imply enabling the
transformation, see also
Not only is this change in the behaviour of vectorize(disable) probably more sensible,
it also helps in implementing options implying transformations.