bug#11866: command date don't accept 61 sec. minutes

[Juergen Heine]

According to The International Earth Rotation Service (IERS) we have
"Leap Seconds" included in our UTC time.

Please refer http://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat .

~ snip ~
 A positive leap second will be introduced at the end of June 2012.
 The sequence of dates of the UTC second markers will be:

 2012 June 30, 23h 59m 59s
 2012 June 30, 23h 59m 60s
 2012 July 1, 0h 0m 0s
~snap~

The command 'date' doesn't calculate it.


Test:

$ date +%s -d "2012-06-30 23:59:60"
date: invalid date `2012-06-30 23:59:60'


Tested version:

date (GNU coreutils) 8.5
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by David MacKenzie.

-- 
Juergen 'sysdef' Heine, address@hidden