Add back a sacrificial $.attrFn object.

Originally removed in 86b775d as part of the enhancement that allows $(html, props) to use any $.fn method.

Although $.attrFn is undocumented it appears to be a poorly kept secret. jQuery Mobile 1.1 is using it and it's the topic of several blog/StackOverflow posts. Leave an empty object here as a dumpster for now, but it's coming out for good in 1.9.

src/attributes.js

@@ -282,6 +282,9 @@ jQuery.extend({
		}
	},

	// Unused in 1.8, left in so attrFn-stabbers won't die; remove in 1.9
	attrFn: {},

	attr: function( elem, name, value, pass ) {
		var ret, hooks, notxml,
			nType = elem.nodeType;