Bug 88352 Operation supports leaks contexts via action handler
I20050315-1100 Susan, this is a different leak from the one that I reported. Test Case: 1. open text editor 2. close text editor ==> DefaultUndoManager is leaked due to undo/redo actions handlers still holding on to the context.
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/IUndoableOperation.java
* @return <code>true</code> if the operation can be executed;
	 *         <code>false</code> otherwise.
	 */
	boolean canExecute();
	/**
	 * <p>
	 * Returns whether the operation can be redone in its current state.
	 * 
	 * <p>
	 * Note: This method may be used to enable UI commands, so the computation
	 * must be fast. If necessary, this method can be optimistic in its
	 * computation and return an error status during the actual redo if it is
	 * determined later that the operation cannot actually redo.
	 * 
	 * @return <code>true</code> if the operation can be redone;
	 *         <code>false</code> otherwise.
	 */
	boolean canRedo();
	/**
	 * <p>
	 * Returns whether the operation can be undone in its current state.
	 * 
	 * <p>
	 * Note: This method may be used to enable UI commands, so the computation
	 * must be fast. If necessary, this method can be optimistic in its
	 * computation and return an error status during the actual undo if it is
	 * determined later that the operation cannot actually undo.
	 * 
	 * @return <code>true</code> if the operation can be undone;
	 *         <code>false</code> otherwise.