libpsdxx [FEATURE]: add test mode -tab to testpsdxx
The log_frequency scale cannot contain exactly the requested number of values for the lowest decade. This test mode allows to check whether the higher value decades are affected by this. They are not. The reason for not producing the requested number of value is, that the smallest frequency on the logarithmic scale than would be smaller than the smallest value on the linear scale. So log_frequency lets the smallest value of the logarithmic scale be as small as the smallest value of the linear scale, but not smaller.