fix #632 Flash transport issues

1) IO.swf was requested from the wrong path when Aria.rootFolderPath
was changed, hence no cross-domain requests were possible.

2) If cross-domain requests for multiple physical files were queued quickly
one after each other, before the Flash transport was loaded (e.g. loading
a template + controller in one `Aria.load` call), then only one of those
requests was actually issued over the network.