Some systems do not deliver SIGPIPE to shell pipeline writers when the
downstream reader has exited. So, also check for errors from
/bin/printf. I fixed this for OpenBSD 6.0 but I think it will also
fix posh on Linux.
Replace some blind timeouts with actual synchronization.
Improve performance on some slow tests.
Tweak some of the remaining timeouts.
This still isn't good enough to get 'make -j9 check'
working reliably on Cygwin for me; I think some Cygwin/
Windows scheduling issues remain.
John Hood