Problems with snd-duration

[To: letz@rd.grame.fr]

simple-readin doesn't crash for me, but I bet the problem
is in the line:

(if two-chans (outb i out-sig-b) (outb i out-sig-a))

which should be:

(if two-chans (outb i out-sig-b))

CLM has changed a lot since Nicky wrote that tutorial,
so I should work through it and update it.  I think
most of the instruments can also be found in the clm
documentation (clm.html) or in the example instruments
in clm.tar.gz -- I test these before every "release"
so they're up-to-date.