ALT_HOME:

DCC keeps its config files in its home directory but writes
status and database files there as well.  This latter point
means that the FreeBSD default home directory for DCC,
/usr/local/dcc, cannot be mounted read-only.

DCC's default home dir of /var/dcc breaks FreeBSD hierarchy
conventions, but allows for a read-only /usr.

Setting ALT_HOME on will set DCC's home to /var/dcc, but keep
its binaries in /usr/local/dcc/libexec.  Since this also means
DCC's config files will be in /var/dcc, for convenience a soft
link from /usr/local/etc/dcc to /var/dcc may be created.

Note also that dccifd's default socket location is DCC's home,
so if /var/dcc is used for the home, then programs like
SpamAssassin may need to be explicitly told where to find
dccifd's socket.