Phaser.StageScaleMode has been renamed to ScaleManager and moved from the system folder to the core folder. It's still available under game.scale.

If your game references the old Phaser.StageScaleMode consts like SHOW_ALL you need to update them to Phaser.ScaleManager, i.e. Phaser.ScaleManager.SHOW_ALL.
All of the Project Templates have been updated to reflect the above change.

src/core/StateManager.js

@@ -37,6 +37,18 @@ Phaser.StateManager = function (game, pendingState) {
         this._pendingState = pendingState;
     }
 
+    /**
+    * @property {boolean} _clearWorld - Clear the world when we switch state?
+    * @private
+    */
+    this._clearWorld = false;
+
+    /**
+    * @property {boolean} _clearCache - Clear the cache when we switch state?
+    * @private
+    */
+    this._clearCache = false;
+
     /**
     * @property {boolean} _created - Flag that sets if the State has been created or not.
     * @private
@@ -228,7 +240,27 @@ Phaser.StateManager.prototype = {
         if (typeof clearWorld === "undefined") { clearWorld = true; }
         if (typeof clearCache === "undefined") { clearCache = false; }
 
-        if (this.game.isBooted === false)
+        if (this.checkState(key))
+        {
+            //  Place the state in the queue. It will be started the next time the game loop starts.
+            this._pendingState = key;
+            this._clearWorld = clearWorld;
+            this._clearCache = clearCache;
+
+            if (arguments.length > 3)
+            {
+                this._args = Array.prototype.splice.call(arguments, 3);
+            }
+
+            //  Already got a state running?
+            if (this.current)
+            {
+                this.onShutDownCallback.call(this.callbackContext, this.game);
+            }
+        }
+
+
+/*        if (this.game.isBooted === false)
         {
             this._pendingState = key;
 
@@ -251,7 +283,6 @@ Phaser.StateManager.prototype = {
                 this._args = [];
             }
         }
-
         if (arguments.length > 3)
         {
             this._args = Array.prototype.splice.call(arguments, 3);
@@ -305,6 +336,7 @@ Phaser.StateManager.prototype = {
             //  No init? Then there was nothing to load either
             this.game.loadComplete();
         }
+        */
 
     },
     
@@ -323,6 +355,64 @@ Phaser.StateManager.prototype = {
     * @param {string} key - The key of the state you want to check.
     * @return {boolean} Description.
     */
+    preUpdate: function () {
+
+        if (this._pendingState && this.game.isBooted)
+        {
+            //  Already got a state running?
+            if (this.current)
+            {
+                this.onShutDownCallback.call(this.callbackContext, this.game);
+            }
+
+            if (this._clearWorld)
+            {
+                this.game.tweens.removeAll();
+
+                this.game.world.destroy();
+
+                if (this._clearCache === true)
+                {
+                    this.game.cache.destroy();
+                }
+            }
+
+            this.setCurrentState(this._pendingState);
+
+            if (this.onPreloadCallback)
+            {
+                this.game.load.reset();
+                this.onPreloadCallback.call(this.callbackContext, this.game);
+
+                //  Is the loader empty?
+                if (this.game.load.totalQueuedFiles() === 0)
+                {
+                    this.game.loadComplete();
+                }
+                else
+                {
+                    //  Start the loader going as we have something in the queue
+                    this.game.load.start();
+                }
+            }
+            else
+            {
+                //  No init? Then there was nothing to load either
+                this.game.loadComplete();
+            }
+
+            this._pendingState = null;
+        }
+
+    },
+
+    /**
+    * Checks if a given phaser state is valid. A State is considered valid if it has at least one of the core functions: preload, create, update or render.
+    *
+    * @method Phaser.StateManager#checkState
+    * @param {string} key - The key of the state you want to check.
+    * @return {boolean} true if the State has the required functions, otherwise false.
+    */
     checkState: function (key) {
 
         if (this.states[key])
@@ -330,18 +420,13 @@ Phaser.StateManager.prototype = {
             var valid = false;
 
             if (this.states[key]['preload']) { valid = true; }
-
-            if (valid === false && this.states[key]['loadRender']) { valid = true; }
-            if (valid === false && this.states[key]['loadUpdate']) { valid = true; }
-            if (valid === false && this.states[key]['create']) { valid = true; }
-            if (valid === false && this.states[key]['update']) { valid = true; }
-            if (valid === false && this.states[key]['preRender']) { valid = true; }
-            if (valid === false && this.states[key]['render']) { valid = true; }
-            if (valid === false && this.states[key]['paused']) { valid = true; }
+            if (this.states[key]['create']) { valid = true; }
+            if (this.states[key]['update']) { valid = true; }
+            if (this.states[key]['render']) { valid = true; }
 
             if (valid === false)
             {
-                console.warn("Invalid Phaser State object given. Must contain at least a one of the required functions.");
+                console.warn("Invalid Phaser State object given. Must contain at least a one of the required functions: preload, create, update or render");
                 return false;
             }
 
@@ -373,6 +458,7 @@ Phaser.StateManager.prototype = {
         this.states[key].math = this.game.math;
         this.states[key].sound = this.game.sound;
         this.states[key].scale = this.game.scale;
+        this.states[key].state = this;
         this.states[key].stage = this.game.stage;
         this.states[key].time = this.game.time;
         this.states[key].tweens = this.game.tweens;