libseed-list module import suggestion

[Jonatan Liljedahl <lijon kymatica com>]

Currently, importing another JS file imports all toplevel variables. 
This is not very nice, since you can't have private stuff without 
resorting to some hack like this:

var _exports = (function() {
    var x = 123;
    var y = 42;
    var f = function() { print(x) };

    return {
        y:y,
        f:f
    }
})();

for(var k in _exports) {
    this[k] = _exports[k];
}

I suggest that if a variable EXPORTS is found, only the symbols listed 
in it will be exported:

  EXPORTS=[foo,bar,x,y];

seed_importer_handle_file() would then do something like this:

  if global.EXPORTS exist and isArray:
     exports = newEmptyObject()
     for each s in EXPORTS:
        exports[s] = global[s]
  else:
     exports = global

  return exports

One could additionally have a naming convention where symbols prefixed 
with underscore is ignored unless EXPORTS is defined.

What do you think?

/Jonatan