Fixed issue 104 and added test. Changed method to use ToString instead of casting

Author: grantfar

src/LitJson/JsonMapper.cs

@@ -782,7 +782,7 @@ private static void WriteValue (object obj, JsonWriter writer,
             if (obj is IDictionary) {
                 writer.WriteObjectStart ();
                 foreach (DictionaryEntry entry in (IDictionary) obj) {
-                    writer.WritePropertyName ((string) entry.Key);
+                    writer.WritePropertyName (entry.Key.ToString());
                     WriteValue (entry.Value, writer, writer_is_private,
                                 depth + 1);
                 }

test/JsonMapperTest.cs

@@ -306,6 +306,22 @@ public void ExportEnumsTest ()
             Assert.AreEqual ("{\"FavouritePlanet\":1,\"Band\":9}", json);
         }
 
+        [Test]
+        public void ExportEnumDictionaryTest()
+        {
+            Dictionary<Planets, int> planets = new Dictionary<Planets, int>();
+            
+            planets.Add(Planets.Jupiter, 5);
+            planets.Add(Planets.Saturn, 6);
+            planets.Add(Planets.Uranus, 7);
+            planets.Add(Planets.Neptune, 8);
+            planets.Add(Planets.Pluto, 9);
+            
+            string json = JsonMapper.ToJson(planets);
+
+            Assert.AreEqual("{\"Jupiter\":5,\"Saturn\":6,\"Uranus\":7,\"Neptune\":8,\"Pluto\":9}", json);
+        }
+
         [Test]
         public void ExportObjectTest ()
         {