title: addAttr method on pymel objects
body: <p>I can't seem to utilize the addAttr method correctly. I'm using the same arguments as when I call from pymel.core but it's not giving me the same results.</p>
  
  <p>I'm trying to add a custom message attribute so I can easily search for certain types of objects later. When I do it from pymel.core and include the same object reference as an argument, it works fine.</p>
  
  <pre><code>#get object reference
  test_object = pm.ls(sl=1)[0]
  
  #this one spits out an error
  test_object.addAttr(longName = 'custom', attributeType = 'message')
  
  #this one works fine
  pm.addAttr(test_object, longName = 'custom', attributeType = 'message')
  </code></pre>
  
  <p>I keep getting this error
  Error: TypeError: file  line 1: addAttr() takes exactly 2 arguments (1 given)
  What additional argument is it looking for when I use it this way? I am clearly missing something obvious about how methods work but I can't figure it out.</p>