#2 Add --lifetime option in slptool

[Jean-Michel Dault]

By default, slptool register sets the lifetime to
65535, and there is no way to change that.

I'm using SLP to provide auto-discovery of terminal
servers, and implement some primitive failover.
Terminal servers register and unregister themselves
every 5 minutes, so if a server is down, it doesn't
appear to SLP clients.

I provide a patch that adds a configurable --lifetime
option, it's quick, ugly, and does no checking, but it
works for me.

Tell me what you think.

[Jean-Michel Dault]

Adds --lifetime option to slptool