some improvements to auth/user_object.rst

* take advantage of intersphinx... add 'free' links to Pyramid docs
* mention availability of the new method earlier
* displaying linenos for 1-liners is overkill
* no need to ask for Python highlighting; it's automatic
* use the more specific 'deprecated' directive, instead of the more
  generic 'note' directive
* add a missing comma (also to pylons/exceptions.rst)