Merge tag '0.66'

This brings in the rest of the 0.66 branch, including some changes new
on master.

Conflicts:
        doc/plink.but
        sshrsa.c

(The conflicts were both trivial: in one, the addition of an extra
parameter to rsa2_newkey on master happened on the line next to 0.66's
addition of a check for NULL return value, and in the other, I'd got
the version number in the plink -h transcript messed up on master.)

sshrsa.c

@@ -773,6 +773,8 @@ static int rsa2_pubkey_bits(const struct ssh_signkey *self,
     int ret;
 
     rsa = rsa2_newkey(self, (const char *) blob, len);
+    if (!rsa)
+	return -1;
     ret = bignum_bitcount(rsa->modulus);
     rsa2_freekey(rsa);