* Add multiple yang support also for obsolete versions

* This means that files and datastores supporting modstate also looks for deleted or updated yang modules.
  * A stricter binding which gives error if loading outdated YANG file does not exist.
* Stricter yang checks: you cannot do get-config on datastores that have obsolete YANG
* Added xerr output parameter to `xmldb_get0()`

lib/src/clixon_yang.c

@@ -452,7 +452,7 @@ ys_new(enum rfc_6020 keyw)
  * @retval    -1    Error
  * @see ys_free
  */
-static int 
+int 
 ys_free1(yang_stmt *ys,
 	 int        self)
 {
@@ -708,6 +708,20 @@ yn_insert(yang_stmt *ys_parent,
     return 0;
 }
 
+/*! Variant of yn_insert where parent is not set
+ */
+int
+yn_insert1(yang_stmt *ys_parent, 
+	   yang_stmt *ys_child)
+{
+    int pos = ys_parent->ys_len;
+
+    if (yn_realloc(ys_parent) < 0)
+	return -1;
+    ys_parent->ys_stmt[pos] = ys_child;
+    return 0;
+}
+
 /*! Iterate through all yang statements from a yang node 
  *
  * @param[in] yparent  yang statement whose children should be iterated