SIGPIPE issue

[willghatch]

A pipeline like yes | head -n 1 should make yes return 141 because it gets sigpipe. But in Rash it returns 1 and prints a message to stderr about a broken pipe. This is inherited from Racket's subprocess function. I haven't yet figured out quite where this is handled or why this behavior is present. I guess it's probably somewhere in the implementation of subprocess or the rktio layer. But at the moment I don't have time to figure it out.