(PHP 4 = 4.0.2)
Returns an array with the key sizes supported by the
specified algorithm. If it returns an empty array then all
key sizes between 1 and mcrypt_module_get_algo_key_size() are
supported by the algorithm. The optional lib_dir parameter can contain the
location where the mode module is on the system.
See also mcrypt_enc_get_supported_key_sizes() which
is used on open encryption modules.