Add regression test for RFC850 parsing

Although not supported directly by chrono, users should be able to
specify the RFC850 format and expect it to parse properly. RFC850 is
important since HTTP/1.1 specifies

    HTTP-date = rfc1123-date | rfc850-date | asctime-date

src/format/parse.rs

@@ -635,6 +635,25 @@ fn test_rfc2822() {
     };
 }
 
+
+
+#[cfg(test)]
+#[test]
+fn parse_rfc850() {
+    use ::{UTC, TimeZone};
+
+    static RFC850_FMT: &'static str =  "%A, %d-%b-%y %T GMT";
+
+    let dt_str = "Sunday, 06-Nov-94 08:49:37 GMT";
+    let dt = UTC.ymd(1994, 11, 6).and_hms(8, 49, 37);
+
+    // Check that the format is what we expect
+    assert_eq!(dt.format(RFC850_FMT).to_string(), dt_str);
+
+    // Check that it parses correctly
+    assert_eq!(Ok(dt), UTC.datetime_from_str("Sunday, 06-Nov-94 08:49:37 GMT", RFC850_FMT));
+}
+
 #[cfg(test)]
 #[test]
 fn test_rfc3339() {