First of all IANAL. libftp-5.0.1.modified.by.in/FtpFilenameChecker.c from upstream says: "This library is desined for free, non-commercial software creation. [..]" LICENSE.TXT is a mixture of BSD-4 and some individual statements. But might be reduced to BSD-4 in fact. I am not sure, if the upstream violates the other licenses, but to my understanding we should add attention to "non commercial".
http://gitweb.gentoo.org/repo/gentoo.git/commit/?id=cd5dd4d193ca150567eedc2d5760ea471d8d7041