Bug 172000 [Wizards] WizardNewFileCreationPage should support overwriting existing resources
In the WizardNewFileCreationPage, there should be a method to set allowExistingResources flag for ResourceAndContainerGroup member. It is useful when both "create" and "renew/overwrite" operations are meaningful for a wizard.
bundles/org.eclipse.ui.ide/extensions/org/eclipse/ui/dialogs/WizardNewFileCreationPage.java
* 
	 * @param value
	 *             The file extension without the '.' prefix 
	 *             (e.g. 'java', 'xml') 
	 * @since 3.3
	 */
	public void setFileExtension(String value) {
		if (resourceGroup == null) {
			initialFileExtension = value;
		} else {
			resourceGroup.setResourceExtension(value);
		}
	}
	
	/**
	 * Checks whether the linked resource target is valid. Sets the error
	 * message accordingly and returns the status.
	 * 
	 * @return IStatus validation result from the CreateLinkedResourceGroup
	 */
	protected IStatus validateLinkedResource() {
		IPath containerPath = resourceGroup.getContainerFullPath();
		IPath newFilePath = containerPath.append(resourceGroup.getResource());
		IFile newFileHandle = createFileHandle(newFilePath);
		IStatus status = linkedResourceGroup
				.validateLinkLocation(newFileHandle);
		if (status.getSeverity() == IStatus.ERROR) {
			if (firstLinkCheck) {
				setMessage(status.getMessage());
			} else {