Add median to icmppingsec check...

When using an icmppingsec check:

icmppingsec[,5,1000,1472,1000,avg]

It would be really nice if 'median' was an option. It's possible for one dropped packet, or a very slow single ping check to skew the average terribly. Use of median would solve this problem well. This should be trivial, but it would go a long way toward improving the quality of the value.