Implement my experimental arcfour modes. The 256-bit version is disabled

until I can test it against someone else's implementation.

[originally from svn r5633]

settings.c

@@ -18,6 +18,7 @@ static const struct keyval ciphernames[] = {
     { "blowfish",   CIPHER_BLOWFISH },
     { "3des",	    CIPHER_3DES },
     { "WARN",	    CIPHER_WARN },
+    { "arcfour",    CIPHER_ARCFOUR },
     { "des",	    CIPHER_DES }
 };