1.0.42.41: use poll(2) instead of select(2) in SYSREAD-MAY-BLOCK-P

1.0.42.41: use poll(2) instead of select(2) in SYSREAD-MAY-BLOCK-P

 Calling select() with a single FD is just waste.

 This also means that we don't use select() outside of serve-event,
 paving way to having more fds open than FD_SETSIZE allows.