Move focus() and blur() into HTMLElement proto

The current implementations of `focus` and `blur` aren't up-to-spec. Moving them into `HTMLElement` will be a step in the right direction. See #956
They were failing, so I went and dug a little deeper. These lines were also removed in https://github.com/markelog/sizzle/commit/d33373d608da1b7f7997967d8e1a78310738c6bb per https://github.com/jquery/sizzle/issues/163