fixed a comment applied a patch from Michael Day to add a new function

* xmlsave.c: fixed a comment
* xinclude.c include/libxml/xinclude.h: applied a patch from Michael Day
  to add a new function providing the _private field for the generated
  parser contexts xmlXIncludeProcessFlagsData()
Daniel
diff --git a/xmlsave.c b/xmlsave.c
index e596c58..6e129a8 100644
--- a/xmlsave.c
+++ b/xmlsave.c
@@ -1570,7 +1570,7 @@
 /**
  * xmlSaveTree:
  * @ctxt:  a document saving context
- * @node:  a document
+ * @node:  the top node of the subtree to save
  *
  * Save a subtree starting at the node parameter to a saving context
  * TODO: The function is not fully implemented yet as it does not return the