removed iconv_set_encoding()
Strings::random uses openssl_random_pseudo_bytes, mcrypt_create_iv or /dev/urandom when is available.

- openssl_random_pseudo_bytes is not used on Windows for PHP < 5.4, because is terrible slow.
- mcrypt_create_iv() crashes with „Fatal error: mcrypt_create_iv(): Could not gather sufficient random data“ in PHP 5.3.3 on Windows