Description:
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In the documentation for substr_count there is a note that says: "Note: This function doesn't count overlapped substrings. See the example below! ". mb_substr_count does not replicate this behaviour, and as mb_substr_count can overload substr_count I think it should.

Reproduce code:
---------------
<?php
$string_ascii = 'abcabcabc';
echo "mb_substr_count: ";
var_dump(mb_substr_count($string_ascii, 'abcabc')); //needle overlaps in haystack
echo "substr_count:    ";
var_dump(substr_count($string_ascii, 'abcabc'));
?>

Expected result:
----------------
mb_substr_count: int(1)
substr_count:    int(1)


Actual result:
--------------
mb_substr_count: int(2)
substr_count:    int(1)