SNMP Alarm Support

I wanted the option to exist only for the case where snmp_ip is set to something. This is different from the previous cases (though both depend on left to right expression evaluation). Initially I had this as an "if", but collapsed it to match the style of the other cases. I'll change it back to an "if" to make it safer.

BTW, it is probably a good thing there is no "set -e" in this file...
http://serverfault.com/questions/143445/what-does-set-e-do-and-why-might-it-be-considered-dangerous