proftpd-dfsg - security update

Vadim Melihow discovered that in proftpd-dfsg, an FTP server, the
mod_copy module allowed unauthenticated users to copy files around on
the server, and possibly to execute arbitrary code.

For the oldstable distribution (wheezy), this problem has been fixed
in version 1.3.4a-5+deb7u3.

For the stable distribution (jessie), this problem has been fixed in
version 1.3.5-1.1+deb8u1.

For the testing distribution (stretch) and unstable distribution
(sid), this problem has been fixed in version 1.3.5-2.

We recommend that you upgrade your proftpd-dfsg packages.