Disk Queue Stats - Average Ages Incorrect

A customer reported that they were seeing a discrepancy between the Average Age Disk Queue Statistics in the GUI and the data available via cbstats.

On investigation, the calculations are using the total number of items in a bucket, rather than the number of items in the disk queue to work out the average age of those items, giving some very small results (in the order of microseconds).

I have attached a patch which uses what I believe to the be the correct values. I've tested this and it gives more appropriate results (i.e. values for average age in tenths of seconds).