String validation fails on string length

In the function _civicrm_api3_validate_string() (api/v3/utils.php)

The code to count the string length is strlen($value), which count bytes instead of chars. That means non-utf8 strings are not handled because in most cases non-utf8 char takes 2 bytes.

This has a lot of consequences because this function is used multiple times, the most obvious is for exemple we can't create a contact using the API if the name is on 128 chars with at least one accent (é, è, ...)

This affects only the API, "native" forms are ok.