Refine media state machine methods.

* state( id ) becomes setState( id )
* get( id ) becomes state( id )
* state() stays the same
* previous() becomes lastState()

Props koopersmith
fixes #22652


git-svn-id: http://core.svn.wordpress.org/trunk@22952 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/custom-header.js

@@ -40,7 +40,7 @@
 				});
 			});
 
-			frame.state('library');
+			frame.setState('library');
 		});
 	});
 }(jQuery));