timeout: round timeouts up

timeout: round timeouts up

This handles timeouts like 16777216.000000001 correctly;
formerly the subsecond part of that timeout was ignored.
* bootstrap.conf (gnulib_modules): Add fenv-rounding, signbit.
* src/local.mk (src_timeout_LDADD): Append $(FENV_ROUNDING_LIBM).
* src/timeout.c: Include fenv.h, math.h.
Don’t include xstrtod.h, as xstrtod’s checking now gets in the way.
(parse_duration): Round up when calling cl_strtod.
Check for -1e-1000.  Don’t double-round 1e-9.
* tests/timeout/timeout-parameters.sh: Test for -0.1,
-1e-1000, 1e-1000.