$last_day = date ('t', mktime(1,1,1,$month,1,$year));
if (($year == '2000') and ($month == '02'))
    {$last_day = 29;}

/* for building a calendar, I needed a loop from 1 to last_day_in_month
checkdate(..) returned correctly 29 for Feb 2000 as last valid day 
getting straight at the last day using date('t',...) - the script above 
returns 28 days
Of course, the "fix" is easy, but better fix the function internally:

Any year evenly divisible by 400 is a leap year!

*/