special s6-svscan/perp(d) catch-all logger service option

[Jeff <sysinit@yandex.com>]

hello,

i am a new subscriber to this mailing list.

i saw that daemontools-encore svscan provides an option to
specify a special catch-all logging service for svscan and its child
supervise processes:

svscan [ directory ] [ log-service ]

If the 'log-service' option is specified and the named subdirectory
exists, svscan starts the service found there and redirects its output
through it. This service is started before any other (since it is the very
important catch-all logger for (among others) svscan's own output).

it would be very nice for s6(-svscan) and perp(d) to provide such
functionality too.

this would simplify starting them directly from init(tab) (or use as init stage 2
in the case of s6) to a great extent as they would do their output redirections
by themselves and also supervise this special catch-all logging service
directly which would init free from this additional task. now init has only 
to supervise (and restart) one process (s6-svscan/perpd) instead of 2
(the additional catch-add logger) which of course is much easier to
achieve.

when using s6-svscan for init stage 2 this would also simplify the
stage 1 script greatly since it can just directly exec into stage 2
now (by using this option) without doing the output redirection
for s6-svscan by itself.

i also think that this can be achieved without too much effort
and since it is an optional feature would not break compatibility
with earlier versions and hence older scripts should still work
without requiring any changes.

kind regards.