yesterday's commit to allow the syntax "gds maskhints <types>", in
which mask hints can be restricted to a specific list of layers
rather than all layers which define mask hints in the cifoutput
rule.
the rule is a normal database rule or a CIF-DRC rule. For the latter,
the flag is used when substituting for escape strings in the "why"
rule explanation to produce the correct value in microns.
Tim Edwards