timeout: support sub-second timeouts
* src/timeout.c (settimeout): A new function to convert
from a floating point duration and call alarm() or
timer_settime() if that's available.
(parse_duration): Return a double rather than unsigned int.
(usage): Mention floating point is supported.
(main): Pass the double to settimeout() rather than
calling alarm() directly with the parsed int.
(cleanup): Likewise.
* doc/coreutils.texi (timeout invocation): Say floating point timeouts
now supported, and mention the caveat with resolution.
* bootstrap.conf: Include the timer-time gnulib module.
* tests/misc/timeout-parameters: Add a test with nanoseconds.
* NEWS: Mention the improvement.