[FIX] (libdatrwxx/thiesdl1): simply add values
This is a legacy commit from before 2015-03-01. It may be incomplete as well as inconsistent. See COPYING.legacy and README.history for details. accept duplicate time stamps as part of normal operation; this is consistent with the behaviour of DL1logger as implemented on 20/03/2014; it is further consistent with the tested behaviour of the ThiesDL1 logger (see note below). Since the statement by Volker König is quite unsatisfactory, Peter Duffner and Thomas Forbriger on 07.11.2012 checked Thies DL1 recordings of several month against manual readings taken directly at the display of the Thies DL1 logger by Peter Duffner for cases where duplicate samples are present in the recorded data. The result is, that the values provided on the data loggers display are obtained, if data values for lines with duplicate time value are added to form the final value for the respective minute.