/*
 * call-seq:
 *   krb5.get_permitted_enctypes
 *
 * Returns a hash containing the permitted encoding types. The key is the
 * numeric constant, with a string description as its value.
 *
 * Example:
 *
 *   krb.get_permitted_enctypes
 *
 *   # Results:
 *   {
 *      1  => "DES cbc mode with CRC-32",
 *      2  => "DES cbc mode with RSA-MD4",
 *      3  => "DES cbc mode with RSA-MD5"}
 *      16 => "Triple DES cbc mode with HMAC/sha1",
 *      17 => "AES-128 CTS mode with 96-bit SHA-1 HMAC",
 *      18 => "AES-256 CTS mode with 96-bit SHA-1 HMAC",
 *      23 => "ArcFour with HMAC/md5"
 *   }
 */
static VALUE rkrb5_get_permitted_enctypes(VALUE self){