Prevent package from removal

[Floris <jkfloris@dds.nl>]

now the libstdc++6 transition is going on $ sudo apt-get dselect-upgrade  
is happy when I remove gdm3, gnome-shell and a lot of other packages. Is  
there a setting to prevent packages from un-installing? Like the big  
warning when you try to delete the base-files package.

Thanks,

floris