Graphics fix for old OSes

CloverApp/Clover/SettingsView.swift

@@ -9,6 +9,7 @@
 import Cocoa
 
 class LITabView: NSTabView {
+  private var drawBack : Bool = false
   var tabIndex: Int = 0
   var lastTabIndex: Int {
     get {
@@ -17,6 +18,18 @@ class LITabView: NSTabView {
       self.tabIndex = newValue
     }
   }
+  
+  override var allowsVibrancy: Bool {
+    return false
+  }
+  
+  override var drawsBackground: Bool {
+    get {
+      return false
+    } set {
+      self.drawBack = false
+    }
+  }
 }
 
 class SoundSlider : NSSlider {