Fixed a mac memory leak when using native sub-menus.

juce_amalgamated.cpp

@@ -270071,6 +270071,7 @@ public:
             NSMenu* sub = createMenu (*iter.subMenu, iter.itemName, topLevelMenuId, topLevelIndex);
             [sub setDelegate: nil];
             [menuToAddTo setSubmenu: sub forItem: item];
+            [sub release];
         }
         else
         {

src/native/mac/juce_mac_MainMenu.mm

@@ -264,6 +264,7 @@ public:
             NSMenu* sub = createMenu (*iter.subMenu, iter.itemName, topLevelMenuId, topLevelIndex);
             [sub setDelegate: nil];
             [menuToAddTo setSubmenu: sub forItem: item];
+            [sub release];
         }
         else
         {