Named modules should be able to require other files

It should be possible to have amdefine `require()` modules from other files when the parent module is explicitly named.

Assume there are two files in the same directory: `foo.js` and `bar.js`.  The pull request make it possible to write code like this:

```
define('foo', function(require) {
  var bar = require('./bar');
});
module.exports = define.require('foo');
```

Without the change from the pull request, amdefine assumes that `bar` is defined inside of `foo.js`.