add failing tests for default function export

The first one seems to be a bug.

The second two are to do with allowing the default token, so perhaps these are not as urgent and could be omitted.


These are in the notes:

https://github.com/rwaldron/tc39-notes/blob/master/es6/2014-06/jun-5-modules.md

The ES grammar is restricted to 1 token look ahead. To revert this to an assignment expression requires 2 token look ahead (or a cover grammar).