applied a documentation patch from Stefan Kost Daniel

* error.c parser.c tree.c: applied a documentation patch from Stefan Kost
Daniel
diff --git a/parser.c b/parser.c
index cb2be96..f05c64f 100644
--- a/parser.c
+++ b/parser.c
@@ -10910,6 +10910,8 @@
  * parsing related global memory allocated for the parser processing.
  * It doesn't deallocate any document related memory. Calling this
  * function should not prevent reusing the parser.
+ * One should call xmlCleanupParser() only when the process has
+ * finished using the library or XML document built with it.
  */
 
 void