Fileinfo extension is not available by default in (at very least) windows

There is 1 use of fileinfo/finfo @

$ ag 'new finfo'

lib/filestorage/file_storage.php

2105:            $finfo = new finfo(FILEINFO_MIME_TYPE);

And overall, it's not problematic... but because of Windows that does not come with it enabled by default and requires action:

http://php.net/manual/en/fileinfo.installation.php

This is leading to > 100 errors in phpunit under windows (standard 7.0.9 download from php downloads site) with error: Error: Class 'finfo' not found

So... ONE OF:

1) of we kill the finfo use above (it used to be optional before 3.3 using class_exists().
2) or we make it a environmental requirement and document it everywhere.

Ciao