Email::FolderType::Mbox(3pm) on Linux

The text 63815afe5f6d, as Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze), Debian 5.0 (Lenny), Debian 4.0 (Etch) shipped it.

class to help Email::FolderType recognise MH mail directories