Make Fileinfo PHP extension a requirement or add warning when missing

[clarkwinkelmann]

We use mime_content_type as fallback to get the MIME type, but we don't require fileinfo PHP extension.

We have a try/catch around mime_content_type so I think this makes the extension optional, but I haven't actually tested what happens when the extension is disabled.

The suggestion is either:

• Make Fileinfo extension required
• Add warning to extension settings page if extension is disabled

FoF Upload should work fine without fileinfo if you use common MIME types. But if you want to use more advanced types including those that might be custom to the specific server, the fallback is useful or even required if you don't want all unknown files to default to the same value.