Bug#891284: xfce4-session: verbose logging is always enabled

[fin4478 fin4478]

Package: xfce4-session
Version: 4.12.1-6

This bug is marked fixed in upstream (see here:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=886855) and it is not
fixed in 4.12.1-6. Version 4.13 package is needed