if (el.classList)
  el.classList.remove(className)
else
  el.className = el.className.replace(new RegExp('(^| )' + className.split(' ').join('|') + '( |$)', 'gi'), ' ')

if (el.classList)
  el.classList.remove(className)
else
  el.className = el.className.replace(new RegExp('(^|\\b)' + className.split(' ').join('|') + '(\\b|$)', 'gi'), ' ')

Fix IE8/9 remove class. Closes #35.