YANG sub module linking + unsupported yang construct + defect fix

Change-Id: I224c8c14ee2111f6844278cb540c48651544f59b
diff --git a/utils/yangutils/src/test/resources/LengthSubStatements.yang b/utils/yangutils/src/test/resources/LengthSubStatements.yang
new file mode 100644
index 0000000..f61f979
--- /dev/null
+++ b/utils/yangutils/src/test/resources/LengthSubStatements.yang
@@ -0,0 +1,13 @@
+module Test {
+    yang-version 1;
+    namespace http://huawei.com;
+    prefix Ant;
+    leaf invalid-interval {
+        type string {
+            length "0..100" {
+                description "length description";
+                reference "length reference";
+            }
+         }
+    }
+}