[#1740] play.Cache.init() is called before the GAE plugin starts patch

The ticket
https://play.lighthouseapp.com/projects/57987/tickets/1740-playcacheinit-is-called-before-the-gae-plugin-starts 
was raised for Play itself but the fix is made in play-gae module.
Gae cached is now initiated onLoad and onApplicationStart

src/play/modules/gae/GAEPlugin.java

@@ -59,6 +59,7 @@ public void onLoad() {
             // Force to PROD mode when hosted on production GAE
             Play.mode = Play.Mode.PROD;
             prodGAE = true;
+            wrapGAECache();
         }
     }
 
@@ -74,16 +75,19 @@ public void onRoutesLoaded() {
 
     @Override
     public void onApplicationStart() {
-        // Wrap the GAE cache
-        if (devEnvironment == null) {
-            Cache.forcedCacheImpl = new GAECache(); 
-        }
-
+        wrapGAECache();
         // Provide the correct JavaMail session
         Mail.session = Session.getDefaultInstance(new Properties(), null);
         Mail.asynchronousSend = false;
     }
 
+    private void wrapGAECache() {
+        // Wrap the GAE cache
+        if (devEnvironment == null && Cache.forcedCacheImpl == null) {
+            Cache.forcedCacheImpl = new GAECache(); 
+        }
+    }
+
     @Override
     public void beforeInvocation() {
         // Set the current development environment if needed