make Software Update Failed dialog less confusing

Patch by Mike Beltzner.
bug=348822
r=mconnor

toolkit/locales/en-US/chrome/mozapps/update/updates.properties

@@ -88,4 +88,4 @@ patchApplyFailure=The Update could not be installed (Patch Apply Failed)
 installPending=Install Pending
 
 updaterIOErrorTitle=Software Update Failed
-updaterIOErrorText=One or more files could not be updated. Please make sure all other applications are closed and that you have permission to modify files, and then restart %S to try again.
+updaterIOErrorMsg=The update could not be installed. Please make sure there are no other copies of %S running on your computer, and then restart %S to try again.

toolkit/mozapps/update/src/nsUpdateService.js.in

@@ -2642,8 +2642,8 @@ UpdatePrompt.prototype = {
             getService(Components.interfaces.nsIStringBundleService);
         var updateBundle = sbs.createBundle(URI_UPDATES_PROPERTIES);
         var title = updateBundle.GetStringFromName("updaterIOErrorTitle");
-        var text = updateBundle.formatStringFromName("updaterIOErrorText",
-                                                     [gApp.name], 1);
+        var text = updateBundle.formatStringFromName("updaterIOErrorMsg",
+                                                     [gApp.name, gApp.name], 2);
         var ww =
             Components.classes["@mozilla.org/embedcomp/window-watcher;1"].
             getService(Components.interfaces.nsIWindowWatcher);