Race condition w/ loadAdapter

[johansten]

Somewhat related to issue #2.

var googleAuth = new OAuth2('google', {
    client_id:      client_id,
    client_secret:  client_secret,
    api_scope:      scopes.join(' ')
});

googleAuth.authorize(function() {
    /* ... */
});

Both OAuth2 and authorize load the adapter.

OAuth2 doesn't set the source config until after the adapter is loaded. Sometimes the loadAdapter() callback in authorize is called before the loadAdapter() callback in OAuth2, and when that happens openAuthorizationCodePopup() doesn't have a valid config.

I hacked it by adding a callback to OAuth2, and calling authorize from there, but that's just a hack.

[johansten]

See #39 for a fix.