minor enhancement to prevent comment with unreferenced variable. edited

* genChRanges.py, chvalid.c, include/libxml/chvalid.h: minor
  enhancement to prevent comment with unreferenced variable.
* threads.c xmlreader.c xmlwriter.c: edited some comments to
  improve auto-generation of documentation
* apibuild.py: minor change to an error message
diff --git a/threads.c b/threads.c
index 30a88ed..ac6c8d6 100644
--- a/threads.c
+++ b/threads.c
@@ -432,6 +432,12 @@
 #endif /* HAVE_WIN32_THREADS */
 
 #if defined HAVE_BEOS_THREADS
+/**
+ * xmlGlobalStateCleanup:
+ * @data: unused parameter
+ *
+ * Used for Beos only
+ */
 void xmlGlobalStateCleanup(void *data)
 {
 	void *globalval = tls_get(globalkey);