Update the apt-file cache; fix whitespace

Force an update of the apt-file cache on cluster (Trac: #1490)
so that users don't get prompted for it on first login.

Also, remove some stray whitespace at the end of the file
Prompt for debathena-msmtp-mta

Ask the user whether or not to install debathena-msmtp-mta,
defaulting to 'yes' for workstation and cluster.  (Trac: #1025)