do not mix standard error into standard output for narwhal

narwhal likes to output \e[0m at the very beginning of standard error,
even when given a --no-term option. this makes whatever testem uses
for parsing TAP protocol not recognise the very first passing testcase,
which causes "MISSING TEST" errors.

alternatively one could print a dummy line inside the test runner,
but this solution seems neater.

why did stderr need to be mixed with stdout in the first place anyway?
why does narwhal munge with terminal escapes unasked? how hard is it
to type reset? or better, get your escapes straight in the first place?

javascript kiddies. i could rant more, but this commit message is
already larger than the patch itself.