Daily/Hourly Logfile, Fix of Logfile

As the log.txt, generated by write_log(), becomes very big i've added a possibility to create a new log file each day and each hour.
daily:
log_130915.txt
log_130916.txt

daily & hourly:
log_130916_11.txt
log_130916_12.txt
log_130916_13.txt

hourly (makes no sense in my oppinion)
log_11.txt
log_12.txt


Also I've fixed a small bug with the backtrace info. These lines were without a value.