The man page says they also return 2 for syntax errors and 3 for "fatal
error: out of memory etc", but I don't know how to implement that and
don't need it (or have any reason to believe anyone needs it).
Bug: 29092208
I don't know that anyone cares, but these failures made me think I'd
broken something while testing the -SIGNAL patch.
The -s parsing wasn't taking into account that -s 0 is a special case,
and the -o test was assuming that pkill can tell the difference between
two processes started at roughly the same time. Hopefully there's
higher-resolution data available that can avoid the need for yet another
sleep in the tests.
