Fix more issues with reverse (aka, "show most recent") option.
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.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome