25 January 2013 at 10:21am
(Last edited: 25 January 2013 10:22am),
fileinfo is used for MIME type detection in HTTP::get_mime_type()
The fileinfo detection is only a warning in the installer, so you can still proceed without it.
When fileinfo isn't loaded, a fallback is in place to use a fixed list of MIME types, so you should be okay.