Add accessibility settings check

The AXAPIEnabled method was deprecated in OS X 10.9 (Mavericks).
However, it is necessary here so it can check if the accessibility
settings in OS X 10.8 (Mountain Lion) are enabled. Otherwise, it would
keep asking the user to enable them even when they are enabled.

ShiftIt/ShiftItAppDelegate.m

@@ -368,7 +368,7 @@ - (void)checkAuthorization {
                 }
 
             }
-        } else {
+        } else if (!AXAPIEnabled()){
             // OSX <= 10.8
             NSAlert *alert = [NSAlert alertWithMessageText:NSLocalizedString(@"Authorization Required", nil)
                                              defaultButton:NSLocalizedString(@"Quit", nil)