printf,seq,sleep,tail,timeout: accept current-locale floats

printf,seq,sleep,tail,timeout: accept current-locale floats

These commands now accept floating-point numbers in the
current locale, as well as in the C locale.
Compatibility problem reported by Robert Elz.
* NEWS: Document this.
* bootstrap.conf (gnulib_modules): Add cl-strtod, cl-strtold.
Remove c-strtold.
* doc/coreutils.texi (Floating point, tail invocation)
(printf invocation, timeout invocation, sleep invocation)
(seq invocation): Document this.
* gl/lib/cl-strtod.c, gl/lib/cl-strtod.h, gl/lib/cl-strtold.c:
* gl/modules/cl-strtod, gl/modules/cl-strtold: New files.
* src/printf.c, src/seq.c, src/sleep.c, src/tail.c, src/timeout.c:
Include cl-strtod.h instead of c-strtod.
* src/printf.c (vstrtold):
* src/seq.c (scan_arg, print_numbers):
* src/sleep.c (main):
* src/tail.c (parse_options):
* src/timeout.c (parse_duration):
Use cl_strtold instead of c_strtold.