Fix more issues with reverse (aka, "show most recent") option.
If both -r and -n (number of records) was given (i.e., as called via the web page), then we were still fetching the oldest N records but then presenting those most recent first. Not real useful. Now we use sub-query fu to fetch the most recent N records but still keep those in oldest-to-newest order for processing. Also, removed two-field-order-by hack as sorting on just the timestamp now seems to use the index and no longer does a filesort. Don't generate summary info when the -x (history index) option is given.