Description:
------------
When the $regs argument is provided, mb_ereg will return the length of the matched string. The integer returned though is the byte length of the  string instead of the character length, which seems illogical for a multibyte string function.

Reproduce code:
---------------
<?php
mb_regex_encoding('utf-8');
$string_mb = base64_decode('5pel5pys6Kqe44OG44Kt44K544OI44Gn44GZ44CCMDEyMzTvvJXvvJbvvJfvvJjvvJnjgII=');

$regex = '^.*?[[:blank:]]?[[:punct:][:digit:]]+\.?$';

echo "\nMultibyte String without \$regs arg:\t";
var_dump(mb_ereg($regex, $string_mb));
echo "Multubyte String with \$regs arg:\t";
var_dump(mb_ereg($regex, $string_mb, $regs_mb));
echo "Character length of matched string:\t";
var_dump(mb_strlen($regs_mb[0], 'utf-8'));
?>

Expected result:
----------------
Multibyte String without $regs arg:	int(1)
Multubyte String with $regs arg:	int(21)
Character length of matched string:	int(21)

Actual result:
--------------
Multibyte String without $regs arg:	int(1)
Multubyte String with $regs arg:	int(53)
Character length of matched string:	int(21)