Conflicts with generated default export names #72

Found while working through #66 – bit of a tricky case, but is possibly superseded by #71, so am just going to leave this test case here:

// main.js
import foo from './foo';

assert.equal( foo(), 'not actually foo' );

// foo.js
export default notActuallyFoo;

function notActuallyFoo () {
  return 'not ' + foo();
}

function foo () {
  return 'actually foo';
}

The notActuallyFoo function gets aliased as foo (because of import foo...), and ends up calling itself, blowing the stack.