Another thread-unsafe date formatter

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@739865 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/util/DateUtils.java

@@ -221,7 +221,9 @@ public final class DateUtils {
             tzMarker.append("0");
         }
         tzMarker.append(minutes);
-        return DATE_HEADER_FORMAT.format(cal.getTime()) + tzMarker.toString();
+        synchronized (DATE_HEADER_FORMAT) {
+            return DATE_HEADER_FORMAT.format(cal.getTime()) + tzMarker.toString();
+        }
     }
 
     /**