A bulk of changes to calculate statistical values corresponding to
DCS DPs according to the number of values ('nentries', hereafter)
falling in the time interval [DAQ_time_start, DAQ_time_end]:
- if (nentries > 1): considering only them
- if (nentries = 1): considering the only entry in this interval, plus
the measurement immediately before DAQ_time_start
- if (nentries = 0): considering only the entry immediately before DAQ_start_time
and the one immediately after DAQ_time_end