Almost working draft of basic undo coalescence

lib/ace/undomanager.js

@@ -63,6 +63,9 @@ var UndoManager = function() {
     this.execute = function(options) {
         var deltas = options.args[0];
         this.$doc  = options.args[1];
+        if (options.merge && this.hasUndo()){
+            deltas = this.$undoStack.pop().concat(deltas);
+        }
         this.$undoStack.push(deltas);
         this.$redoStack = [];