Fix setter so IE7/8 can set text of style element

fixes #2265

Our setters brake old IE when setting text of a style element.
This pull request adds a alternative `propertySetters.text` in case the problem exists in the Browser.

Used some ideas from @arian's  fix on his `fix-2265-text branch`.
I wonder if the bug is also with getters, or just with setters. If it's with getters too, then I would do:

propertyGetters.text = (function(getter){
  return function(node){
    return  (node.get('tag') == 'style') ? node.innerHTML : getter(node);
  };
})(propertyGetters.text);