missing field errors displayed original field name instead of renamed

closes #63

tests/test_json.rs

@@ -1,4 +1,4 @@
-#![feature(custom_derive, plugin, test)]
+#![feature(custom_derive, plugin, test, custom_attribute)]
 #![plugin(serde_macros)]
 
 extern crate test;
@@ -1019,3 +1019,26 @@ fn test_missing_field() {
     ))).unwrap();
     assert_eq!(value, Foo { x: Some(5) });
 }
+
+#[test]
+fn test_missing_renamed_field() {
+    #[derive(Debug, PartialEq, Deserialize)]
+    struct Foo {
+        #[serde(rename_deserialize="y")]
+        x: Option<u32>,
+    }
+
+    let value: Foo = from_str("{}").unwrap();
+    assert_eq!(value, Foo { x: None });
+
+    let value: Foo = from_str("{\"y\": 5}").unwrap();
+    assert_eq!(value, Foo { x: Some(5) });
+
+    let value: Foo = from_value(Value::Object(treemap!())).unwrap();
+    assert_eq!(value, Foo { x: None });
+
+    let value: Foo = from_value(Value::Object(treemap!(
+        "y".to_string() => Value::I64(5)
+    ))).unwrap();
+    assert_eq!(value, Foo { x: Some(5) });
+}