Function one_file_name 

fn one_file_name(name: &str) -> String

An attachment’s name as one file in a folder. The core takes any path out of it; Windows also reads “C:x” as a drive, “a:b” as a hidden stream and “CON”, “NUL”… as devices: those characters become “_”, those names get one in front, and the dots and spaces it would drop at the end go.