Keep setFile atomic.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@277641 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/types/AbstractFileSet.java

@@ -210,7 +210,7 @@ public abstract class AbstractFileSet extends DataType
      * @param file the single <code>File</code> included in this
      *             <code>AbstractFileSet</code>.
      */
-    public void setFile(File file) {
+    public synchronized void setFile(File file) {
         if (isReference()) {
             throw tooManyAttributes();
         }