[Mac] Trying to close the Download Manager window (when it's the last open window) asks to confirm quit. r=mconnor

toolkit/content/globalOverlay.js

@@ -11,9 +11,12 @@ function closeWindow(aClose)
       break;
   }
 
+# Closing the last window doesn't quit the application on OS X.
+#ifndef XP_MACOSX
   // If we're down to the last window and someone tries to shut down, check to make sure we can!
   if (windowCount == 1 && !canQuitApplication()) 
     return false;
+#endif
 
   if (aClose)    
     window.close();

toolkit/content/jar.mn

@@ -24,7 +24,7 @@ toolkit.jar:
 *+ content/global/findUtils.js                (findUtils.js)
 *+ content/global/fontpackage.js              (fontpackage.js)
 *+ content/global/fontpackage.xul             (fontpackage.xul)
-+  content/global/globalOverlay.js            (globalOverlay.js)
+*+ content/global/globalOverlay.js            (globalOverlay.js)
 +  content/global/mozilla.xhtml               (mozilla.xhtml)
 *+ content/global/nsDragAndDrop.js            (nsDragAndDrop.js)
 +  content/global/nsTransferable.js           (nsTransferable.js)