dcf77: annotate unexpected bit numbers and values, do not abort execution

dcf77: annotate unexpected bit numbers and values, do not abort execution

Improve robustness of the DCF77 decoder. Cope with "neiter 0 nor 1" bit
values (glitches can break the detection of pulse widths), as well as
unexpected bit numbers (more than 59 pulses per minute, can be a
follow-up error after e.g. glitches break one long pulse into two short
pulses). Do not process this invalid data, do emit error annotations.