PHP APC File Upload Progress Support for IE 7, 8, and 9

I needed file progress support for IE 7, 8, and 9, so I added an "apc" option. When the user has apc enabled and the upload falls back to the iframe mode (< IE9), apc will kick in and update the progress.

- This should not affect modern browsers in any way.
- This can't give a full upload progress indicator so the main progress bar is using the current file's progress.

Not sure if you want to merge this feature or not. I can keep it in a separate fork and maintain it if necessary.