Merge branch 'foolproof_file_redirection_branch' into 'nightly'

Foolproof file redirection

This solves an issue when our internal /attachment/{file_id} links are shortened with an remote shorteners (which caused the /attachment/{file_id} links to be saved to the File table and a thumbnail of a thumbnail being generated)

See merge request !98

diff --cc classes/File.php
Simple merge

diff --cc classes/File_redirection.php
Simple merge