unix: handle POLLERR and POLLHUP in uv__stream_io
unix: handle POLLERR and POLLHUP in uv__stream_io

Fixes a busy loop when the file descriptor emits POLLHUP but not POLLIN
or POLLOUT, e.g. when polling the read end of a pipe and the write end
is closed.

Fixes joyent/node#4923.

unknownbrackets/maxcso,unknownbrackets/maxcso,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,urbit/archaeology2,unknownbrackets/maxcso,urbit/archaeology2,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,urbit/archaeology2