Add a couple more to_json impls.

Author: erickt

src/libstd/json.rs

@@ -510,6 +510,14 @@ impl of to_json for json {
     fn to_json() -> json { self }
 }
 
+impl of to_json for @json {
+    fn to_json() -> json { *self }
+}
+
+impl of to_json for int {
+    fn to_json() -> json { num(self as float) }
+}
+
 impl of to_json for i8 {
     fn to_json() -> json { num(self as float) }
 }
@@ -526,6 +534,10 @@ impl of to_json for i64 {
     fn to_json() -> json { num(self as float) }
 }
 
+impl of to_json for uint {
+    fn to_json() -> json { num(self as float) }
+}
+
 impl of to_json for u8 {
     fn to_json() -> json { num(self as float) }
 }