Fix "append" behaviour for unity project

[nicloay]

-            if (Directory.Exists(dst))
-            {
-                Directory.Delete(dst,true);
+            if (!Directory.Exists(dst))
+            {                
+                DirectoryCopy(src, dst);
+                string fileRelatvePath = string.Format("Unity-iPhone/{0}.lproj/AppiraterLocalizable.strings", locale);
+                proj.AddLocalization("InfoPlist.strings", locale, fileRelatvePath);            
             }
-            DirectoryCopy(src, dst);
-
-            string fileRelatvePath = string.Format("Unity-iPhone/{0}.lproj/AppiraterLocalizable.strings", locale);
-            proj.AddLocalization("InfoPlist.strings", locale, fileRelatvePath);