login-utils: use libc error printing facility

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
textual: improve error messages

Use error printing facilities that add command name in front of the error
message, and add explanation that is part of existing translations.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
line: use util-linux conventions

This change add --help and --version print outs, checking at exit the
stdout write was successful, and as a minor thing the command is made to
use wide char functions to read and write inputs.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
build-sys: hwclock requires -lm

hwclock uses fabs and therefore needs libm, otherwise a linking
error ocurrs when building with -fno-builtin.
lslogins: fix assertion failure for none existing logins

This cange makes the following to retun none-zero value instead of a core
dump.

$ lslogins qwertyuiopasdfghjklzxcvbnm1234567
lslogins: libsmartcols/src/line.c:362: scols_line_get_cell: Assertion `ln' failed.
Aborted (core dumped)

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
lslogins: align usage() and manual with struct option longopts

Short option -G goes together with long option --supp-groups, while
neither of -m or --groups-info has worked in a release so remove them
from usage() and manual.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>