add clear()

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@359225 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/types/resources/BaseResourceCollectionContainer.java

@@ -55,6 +55,20 @@ public abstract class BaseResourceCollectionContainer
         return cache;
     }
 
+    /**
+     * Clear the container.
+     * @throws BuildException on error.
+     */
+    public synchronized void clear() throws BuildException {
+        if (isReference()) {
+            throw noChildrenAllowed();
+        }
+        rc.clear();
+        FailFast.invalidate(this);
+        coll = null;
+        setChecked(false);
+    }
+
     /**
      * Add a ResourceCollection to the container.
      * @param c the ResourceCollection to add.