[9fans] rc for loop exiting from emu on Plan 9

[Anthony Sorace <anothy@gmail.com>]

Trying to help diagnose a race condition in emu, I did this:

for (i in `{seq 1 100}) {echo BEGIN RUN $i ; emu sh -c
/usr/a/bin/sh/emuerr; echo END RUN $i ; echo}

where emuerr is a sh.dis script that raises an exception. on OS X,
using p9p's rc, i get a bunch of stanzas that look like:

BEGIN RUN 4
start
end
start2
OOPS: fail:some error
END RUN 4

except for the run number. running exactly the same command with the
same script on Plan 9, rc gives up after the "OOPS" line. same
behavior on native plan9 and 9vx. i'd expect the behavior seen on OS
X. it's not the exception, either; i get the same behavior if i
replace the entire rc for clause with {emu sh -c date}.

what is rc confused about?