xplist: Plug memory leak when converting PLIST_UID nodes to XML

In node_to_xml nodes of type PLIST_UID are temporarily converted
to a PLIST_DICT for an appropriate XML output. Therefore a PLIST_KEY
and a PLIST_UINT node is created and inserted into the PLIST_DICT
node. Upon completion, the child nodes of the PLIST_DICT node are
detached from the original node and freed, however the data of the
child nodes - the key string and the uint value - are not.
This commit fixes it.
diff --git a/src/plist.c b/src/plist.c
index d20a252..703ac65 100644
--- a/src/plist.c
+++ b/src/plist.c
@@ -91,7 +91,7 @@
     return data;
 }
 
-static void plist_free_data(plist_data_t data)
+void plist_free_data(plist_data_t data)
 {
     if (data)
     {
diff --git a/src/plist.h b/src/plist.h
index 822144d..ad65dea 100644
--- a/src/plist.h
+++ b/src/plist.h
@@ -67,6 +67,7 @@
 plist_t plist_new_node(plist_data_t data);
 plist_data_t plist_get_data(const plist_t node);
 plist_data_t plist_new_plist_data(void);
+void plist_free_data(plist_data_t data);
 int plist_data_compare(const void *a, const void *b);
 
 
diff --git a/src/xplist.c b/src/xplist.c
index e0a76da..8fe3604 100644
--- a/src/xplist.c
+++ b/src/xplist.c
@@ -337,6 +337,7 @@
         for (j = num; j > 0; j--) {
             node_t* ch = node_nth_child(node, j-1);
             node_detach(node, ch);
+            plist_free_data((plist_data_t)((node_t*)ch)->data);
             node_destroy(ch);
         }
         node_data->type = PLIST_UID;