Description:
------------
A DateInterval created with a period that spans zero days reports $days = FALSE rather than 0.

A DateInterval created by subtracting two DateTimes reports $days = 0 correctly.

Test script:
---------------
<?php

// Period of zero days, zero seconds
// $days = FALSE
print_r(new DateInterval('P0Y'));

// Difference of identical timestamps
// $days = 0
print_r(date_diff(new DateTime('@1289997296'), new DateTime('@1289997296')));

Expected result:
----------------
DateInterval Object
(
    [y] => 0
    [m] => 0
    [d] => 0
    [h] => 0
    [i] => 0
    [s] => 0
    [invert] => 0
    [days] => 0
)
DateInterval Object
(
    [y] => 0
    [m] => 0
    [d] => 0
    [h] => 0
    [i] => 0
    [s] => 0
    [invert] => 0
    [days] => 0
)


Actual result:
--------------
DateInterval Object
(
    [y] => 0
    [m] => 0
    [d] => 0
    [h] => 0
    [i] => 0
    [s] => 0
    [invert] => 0
    [days] => 
)
DateInterval Object
(
    [y] => 0
    [m] => 0
    [d] => 0
    [h] => 0
    [i] => 0
    [s] => 0
    [invert] => 0
    [days] => 0
)