doc_comment plugin throws exception for ExportNamedDeclaration node doc

[mrennie]

Consider the following snippet:

 * @param {Object} arg
 */
export function f(arg) {}

If you run that through the doc_comment plugin and exception will be thrown from applyType.

Related Orion bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=495549

This could be related to / or the cause of issue #769

[mrennie]

So it turns out the exception was in some Orion-specific changes we made to support processing JSDoc for exported items.