Flex 3: Upload multiple files via POST with AS3

In my current Abobe Flex project, I needed to upload multple generated files and form fields to a server. UploadPostHelper by Jonathan Marston is a great for uploading one file at time, but sadly I couldn't use (or even modify) it - it's licensed under NonCommercial CC, and my project is a commercial one.

So I had to write my own code which I would like to share with other's (dual-licensed under MPL 1.1 and LGPL 2.1).