#2058 - Move non-uploadify-specific add item logic out of uploader.
- Created item::add_from_upload() to handle the interface with Kohana's uploader and Gallery's item model.
- Used $_FILES to get filename instead of assuming it's substr($temp_file, 10).
- Stripped corresponding code from uploader.  This makes uploader a bit more uploadify-specific.
- No end-user functional changes - works just like before.