New - API: plugin(), plugin.register() and plugin.deregister() methods

- When working with plug-ins such as TableTools, there is no clearly
  defined way at the moment to get at the plug-in instance, with each
  doing it its own way (TableTools as a static function, while Scroller
  attaches itself to the settings object and KeyTable is its own
  intialiser, amoung others...) so I'm introducing these methods to
  unify this.

- plugin() is used by DataTables users to get their plugin instance, for
  example `table.plugin('tabletools')` would get the TableTools
  instance allowing full access to its API.

- plugin.register() and plugin.deregister() are called by the plug-ins
  when they attach themselves to a DataTable. The 'extras' will all need
  to be updated to use this new method.

.datatables-commit-sync

@@ -1 +1 @@
-ddd0e5f5c9509cd8fa5630453cc05c9f68863644
+730e2b88377acb44e9db177e107b9d42ac8bf63f

media/js/jquery.dataTables.js

@@ -6038,7 +6038,7 @@
 	{
 		if ( ! this instanceof _Api ) {
 			throw 'DT API must be constructed as a new object';
-			// or should it do the 'new' for the caller
+			// or should it do the 'new' for the caller?
 			// return new _Api.apply( this, arguments );
 		}
 	
@@ -8241,6 +8241,49 @@
 	} );
 	
 	
+	_api.register( 'plugin()', function ( type ) {
+		var ctx = this.context;
+	
+		if ( ! ctx.length ) {
+			return null;
+		}
+	
+		var plugins = ctx[0].oPlugins[ type ];
+	
+		return ! plugins ?
+			null :
+			plugins.length == 1 ?
+				plugins[0] :
+				plugins;
+	} );
+	
+	_api.register( 'plugin.register()', function ( type, inst ) {
+		return this.iterator( 'table', function ( settings ) {
+			var plugins = settings.oPlugins;
+	
+			if ( ! plugins[ type ] ) {
+				plugins[ type ] = [];
+			}
+	
+			plugins[ type ].push( inst );
+		} );
+	} );
+	
+	_api.register( 'plugin.deregister()', function ( type, inst ) {
+		return this.iterator( 'table', function ( settings ) {
+			var plugins = settings.oPlugins[ type ];
+	
+			if ( plugins ) {
+				var idx = $.inArray( inst, plugins );
+	
+				if ( idx >= 0 ) {
+					plugins.splice( idx, 1 );
+				}
+			}
+		} );
+	} );
+	
+	
 	_api.register( 'destroy()', function ( remove ) {
 		remove = remove || false;
 	
@@ -12616,7 +12659,14 @@
 		 *  @type array
 		 *  @default []
 		 */
-		"aLastSort": []
+		"aLastSort": [],
+	
+		/**
+		 * Stored plug-in instances
+		 *  @type object
+		 *  @default {}
+		 */
+		"oPlugins": {}
 	};
 
 	/**