json module encodes invalid unicode code points in test

[thestinger]

I've had to xfail this test for now to fix str. The problem line is assert_eq!(from_str("\"").

    fn test_read_str() {
        assert_eq!(from_str("\""),
            Err(Error {line: 1u, col: 2u, msg: @~"EOF while parsing string"
        }));
        assert_eq!(from_str("\"lol"),
            Err(Error {line: 1u, col: 5u, msg: @~"EOF while parsing string"
        }));

        assert_eq!(from_str("\"\""), Ok(String(~"")));
        assert_eq!(from_str("\"foo\""), Ok(String(~"foo")));
        assert_eq!(from_str("\"\\\"\""), Ok(String(~"\"")));
        assert_eq!(from_str("\"\\b\""), Ok(String(~"\x08")));
        assert_eq!(from_str("\"\\n\""), Ok(String(~"\n")));
        assert_eq!(from_str("\"\\r\""), Ok(String(~"\r")));
        assert_eq!(from_str("\"\\t\""), Ok(String(~"\t")));
        assert_eq!(from_str(" \"foo\" "), Ok(String(~"foo")));
        assert_eq!(from_str("\"\\u12ab\""), Ok(String(~"\u12ab")));
        assert_eq!(from_str("\"\\uAB12\""), Ok(String(~"\uAB12")));
    }