tagger eval: add POS WC lower bound metric

utils/tagger-eval.py

@@ -135,6 +135,7 @@ class Metric:
 	# as above but metric for POS hits
 	POS_WC = ([Feat.WEAK_POS_HIT], None)
 	POS_SC = ([Feat.STRONG_POS_HIT], None)
+	POS_WC_LOWER = ([Feat.WEAK_POS_HIT, Feat.SEG_NOCHANGE], None) # lower bound for POS WC
 	# separate stats for known and unknown forms
 	KN_WC = ([Feat.WEAK_TAG_HIT, Feat.KNOWN], [Feat.KNOWN])
 	UNK_WC = ([Feat.WEAK_TAG_HIT, Feat.UNKNOWN], [Feat.UNKNOWN])