Add another bug workaround, this one for old OpenSSH (<2.3) servers

which have a strange idea of what data should be signed in a PK auth
request. This actually got in my way while doing serious things at
work! :-)

[originally from svn r2800]

putty.h

@@ -439,7 +439,7 @@ struct config_tag {
     /* SSH bug compatibility modes */
     int sshbug_ignore1, sshbug_plainpw1, sshbug_rsa1,
 	sshbug_hmac2, sshbug_derivekey2, sshbug_rsapad2,
-	sshbug_dhgex2;
+	sshbug_dhgex2, sshbug_pksessid2;
     /* Options for pterm. Should split out into platform-dependent part. */
     int stamp_utmp;
     int login_shell;