Fix min/max for input without type attribute

As noted in https://github.com/jzaefferer/jquery-validation/pull/660#issuecomment-14654613,
input fields without type did not treat min/max numerically.
This happens in jqueryui forms.

For a demonstration see http://jsbin.com/uxigir/1
(As an aside, that demo also shows that I don't know how to make
error messages show up in the right place, but that's unrelated
to this issue)

This commit treats input fields without type like input fields
with type=text.

Adapted test cases accordingly; tested in chromium.