The current implementation of bad-values stores the
attributes per PDL-datatype rather than per pdl object.
When reading in data from different sources with
different bad-data attributes (i.e. badvalue, badflag),
it is very hard to remap all badvalues to a single
badvalue for the whole program.
Making badvalues pdl-properties would simplify the work
with bad-values in PDL a lot, in particular in larger