lib: add poll(2) alias, lazy waiter for poll.

this doesn't provide an ideal behavior of poll(2)/select(2).
lib: update README.md and document for both NUSE and DCE
lib: fix incorrect timeout value calculation for poll(2)/select(2)

timeout value was incorrectly (and internally) converted to absolute jiffies value.
lib: add a wget test. nc test is disabled for a while.
lib: error message with perror
lib: invalid host file descriptor handling during poll/select

must skip unnecessary fd during poll(2).