16 slices per disk instead of 8 previously ; and tidy things a bit

Thanks cd@sentia.nl

for pointing out this evaded the last commit

- new installs wont have existing ifaliases
- updates dont touch /etc
- manual updates of /etc/ should know what they're doing anyway
fwiw, see hostname.if(5) alias functionality has moved here for better
overall network configurability

changed so files are e.g. backups/etc_passwd not backups/_etc_passwd

symbolic links (the -h flag is for compatibility only); millert@ ok

add commented out entry into sysctl.conf for vfs.nfs.iothreads

REMEMBER TO UPDATE YOUR TREE BEFORE REBUILD! This *will* be used shortly.

when the monitor is blanked.

Enable by setting DEBUGLIBS=yes in /etc/mk.conf, then -g libraries will get
installed in /usr/lib/debug.  This directory will be searched first if
gcc is given the -g flag during the link stage.

.. ok deraadt@, millert@

Since /tmp might be a link to /var/tmp, prune at ssh-* or .X11-unix
like the find on /tmp does.

everything fits...