[collectd] swap activity patch

[Jason Pepas]

Hello,

I have created a patch which adds counters for blocks swapped in and out
(like the "si" and "so" columns of vmstat).

here is an example of it running on my asus wl500gd:

http://66.90.185.129/hourly/Nov/10/22/index.html#swap-activity.png

-jason pepas