New: Initialisation option - sortMulti. Allow / disallow multi-coloumn sorting

- Multi-coloumn sorting might not be a feature that everyone wants, so
  the ability to disable it is added in this commit.

- This fixes issue #13.

media/src/core/core.constructor.js

@@ -103,6 +103,7 @@ _fnMap( oSettings.oFeatures, oInit, "bPaginate" );
 _fnMap( oSettings.oFeatures, oInit, "bLengthChange" );
 _fnMap( oSettings.oFeatures, oInit, "bFilter" );
 _fnMap( oSettings.oFeatures, oInit, "bSort" );
+_fnMap( oSettings.oFeatures, oInit, "bSortMulti" );
 _fnMap( oSettings.oFeatures, oInit, "bInfo" );
 _fnMap( oSettings.oFeatures, oInit, "bProcessing" );
 _fnMap( oSettings.oFeatures, oInit, "bAutoWidth" );

media/src/core/core.sort.js

@@ -237,7 +237,7 @@ function _fnSortAttachListener ( settings, attachTo, colIdx, callback )
 			var nextSort;
 
 			// If the shift key is pressed then we are multiple column sorting
-			if ( e.shiftKey ) {
+			if ( e.shiftKey && settings.oFeatures.bSortMulti ) {
 				// Are we already doing some kind of sort on this column?
 				var curr = _pluck( sorting, '0' );
 				var idx = $.inArray( colIdx, curr );

media/src/model/model.defaults.js

@@ -743,6 +743,26 @@ DataTable.defaults = {
 	"bSort": true,
 
 
+	/**
+	 * Enable or display DataTables' ability to sort multiple columns at the
+	 * same time (activated by shift-click by the user).
+	 *  @type boolean
+	 *  @default true
+	 *
+	 *  @dtopt Options
+	 *  @name DataTable.defaults.sortMulti
+	 *
+	 *  @example
+	 *    // Disable multiple column sorting ability
+	 *    $(document).ready( function () {
+	 *      $('#example').dataTable( {
+	 *        "sortMulti": false
+	 *      } );
+	 *    } );
+	 */
+	"bSortMulti": true,
+
+
 	/**
 	 * Allows control over whether DataTables should use the top (true) unique
 	 * cell that is found for a single column, or the bottom (false - default).

media/src/model/model.settings.js

@@ -113,6 +113,14 @@ DataTable.models.oSettings = {
 		 */
 		"bSort": null,
 
+		/**
+		 * Multi-column sorting
+		 * Note that this parameter will be set by the initialisation routine. To
+		 * set a default use {@link DataTable.defaults}.
+		 *  @type boolean
+		 */
+		"bSortMulti": null,
+
 		/**
 		 * Apply a class to the columns which are being sorted to provide a
 		 * visual highlight or not. This can slow things down when enabled since