not starting daemons at boot: ln -s disabled

[Dan Jacobson <jidanni@jidanni.org>]

One way of having some daemons not start at boot (e.g., if we only use
our printer once a year) is to remove certain /etc/rc?.d/ links.

But the downsize is later, unless one keeps records, one isn't quite
sure of just what tampering one has done in /etc/rc?.d/

So in /etc/default/* we can set NO_START_AT_BOOT=1 etc., at least we
can see and comment what we did.

However there still is a way to know what we tampered with in
/etc/rc?.d/: instead of telling the user to just remove some links,
have them instead ln -s to /dev/null or better: /etc/init.d/disabled perhaps,
an empty file mode 555.

And those link manager programs could do the same.

So then one could see clearly that S20cwdaemon -> ../init.d/disabled
etc.  Or use DISABLED for extra clarity.

Not as efficient as removing the link, but at least one can see what
one did later.