Fix xfce4-panel manual for 4.2 (mail checker)

[Rob Lahaye]

- pop3://user:password at server.
+ pop3://user:password at server:port.
+ The port defaults to 110 when omitted.


Two disadvantages of the mailchecker:
1) Password is in clear text, whenever I pop-up the properties.
2) I can't add a launcher to the mailchecker.

Rob.