Description:
------------
iterate an array which included both int(0) and string type key with foreach, and 
compare key and string value, get an error result! 

Test script:
---------------
$test = array(
    'str' => 'str',
    0 => 0,
    1 => 1
);

foreach ($test as $k=>$v) {
    if ('str' == $k)
        echo "$k == str \n";
}

Expected result:
----------------
output 'str == str ' only

Actual result:
--------------
output: 
str == str 
0 == str