last: fix uninitialized length

length was unset when using "last --time-format=iso"

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
last: --time-format=full should do the same like -F

For no reason "full" did something else than "iso" or -F as you
see here:
$ ./last  -f ../tests/ts/last/wtmp.LE  --time-format=full  | grep -A2 "no logout"
torvalds linux        hobby            Mon Aug 26 02:57:08 1991    gone                    - no logout
reboot   system boot  system-name      Wed Aug 28 20:00:00 2013   still                    running
reboot   system boot  system-name      Wed Aug 28 18:00:00 2013 - Wed Aug 28 19:00:00 2013  (01:00)
$ ./last  -f ../tests/ts/last/wtmp.LE  --time-format=iso  | grep -A2 "no logout"
torvalds linux        hobby            1991-08-26T02:57:08+0200   gone - no logout
reboot   system boot  system-name      2013-08-28T20:00:00+0200   still running
reboot   system boot  system-name      2013-08-28T18:00:00+0200 - 2013-08-28T19:00:00+0200  (01:00)
$ ./last  -f ../tests/ts/last/wtmp.LE  -F  | grep -A2 "no logout"
torvalds linux        hobby            Mon Aug 26 02:57:08 1991   gone - no logout
reboot   system boot  system-name      Wed Aug 28 20:00:00 2013   still running
reboot   system boot  system-name      Wed Aug 28 18:00:00 2013 - Wed Aug 28 19:00:00 2013  (01:00)

Also note the useless leading space before "gone"

The only thing which matters is fmt->out width when printing these
strings like "still running". Now ctl->fulltime flag is unsused and
removed.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: add test case for last -time-format=full

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
last: minor cleanup if statements

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
last: avoid leading "-" before "no logout"

This affects option --time-format=notime.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>