IE can't add properties on an attribute-node element, thus we handle it
like text-/comment-nodes.

Only try to get data attributes for a jQuery-wrapped object if it is actually an Element node. Fixes #7524.

Coerce s.url to string before calling replace, since replace is also a method of a Location object. Fixes #7531.

Also added some tests for this attr(name), attr(name, value) and removeAttr(name).

Maintain returning 0px from width/height for disconnected nodes for backwards compat, for now. Fixes #7395.

Removing the conditional was too liberal as now attr() would even work
on plain javascript objects. Keeping a check to make sure it is at least
a DOM Node is appropriate. Using nodeName as in the commit which introduced
the nodeType === 1 check seems plausible.

Ensure that unquoted attribute selectors are quoted (allowing them to go into qSA/matchesSelector properly). Fixes #7216.

Make sure that if an additional load event is triggered (such as an iframe being dynamically injected in DOM ready) the ready event isn't triggered twice. Fixes #7352.