Add useful safe equals for comparing Strings

Author: mythz

src/AndroidClient/client/src/main/java/net/servicestack/client/Utils.java

@@ -529,4 +529,12 @@ public static <K,V> HashMap<K,V> createMap(K k1, V v1, K k2, V v2, K k3, V v3) {
         to.put(k3, v3);
         return to;
     }
+
+    public static boolean equals(String s1, String s2){
+        if (s1 == null)
+            return s2 == null;
+        if (s2 == null)
+            return s1 == null;
+        return s1.equals(s2);
+    }
 }