Allow redundant lines in data files to facilitate merging (#962)

Author: eggrobin

unicodetools/src/main/java/org/unicode/props/PropertyUtilities.java

@@ -31,6 +31,9 @@ public String merge(String first, String second) {
     static final <K, V, M extends Map<K, V>> M putNew(M map, K key, V value) {
         final V oldValue = map.get(key);
         if (oldValue != null) {
+            if (oldValue.equals(value)) {
+                return map;
+            }
             throw new UnicodePropertyException(
                     "Key already present in Map: "
                             + key
@@ -48,6 +51,9 @@ static final <V> UnicodeMap<V> putNew(
         final V oldValue = map.get(key);
         if (oldValue != null && (missingSet == null || !missingSet.contains(key))) {
             if (merger == null) {
+                if (oldValue.equals(value)) {
+                    return map;
+                }
                 throw new UnicodePropertyException(
                         "Key already present in UnicodeMap: "
                                 + Utility.hex(key)