Function proxy

test/babel.js:830–835

(fn)

	  var newType = t.DEPRECATED_KEYS[_type];

	  function proxy(fn) {
	    return function () {
	      console.trace("The node type " + _type + " has been renamed to " + newType);
	      return fn.apply(this, arguments);
	    };
	  }

	  t[_type] = t[_type[0].toLowerCase() + _type.slice(1)] = proxy(t[newType]);
	  t["is" + _type] = proxy(t["is" + newType]);