Dialups should run zwgc

[jdreed]

I'm aware that we've been through this discussion before. However, the more I think about it, not running zwgc on dialups is an artifact of self-selection among Linerva maintainers and barnowl users, and not a real design decision.

I assert that this should be a sysadmin-controlled option, and not a Debathena-controlled option. However, I'll settle for a more verbose message in the dotfiles, which I'll commit anyway, because "This is a dialup, so zwgc is not being run on login." is meaningless to the average Athena user.