We are currently skipping waveform files by inspecting the name of the
file. However, for some Centaur and Pegasus data sets whose station name
match a pattern used to filter waveform files, all their files are
skipped. We fix this problem by checking for waveform channels instead
of waveform files.
A unit test was skipped in this merge request. That test is not fixed because the problem is caused by #160 (closed), a fix for which would be out of scope of this merge request.
