[glib] Add missing Since: tag

[Matthias Clasen <matthiasc src gnome org>]

commit 4b28e6a0084118c78c177da3f66c8005498b9873
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Dec 3 14:48:35 2010 -0500

    Add missing Since: tag
    
    g_simple_async_result_is_valid was added in 2.20.
    
    Bug 636351

 gio/gsimpleasyncresult.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gio/gsimpleasyncresult.c b/gio/gsimpleasyncresult.c
index 402a737..2166bea 100644
--- a/gio/gsimpleasyncresult.c
+++ b/gio/gsimpleasyncresult.c
@@ -904,6 +904,8 @@ g_simple_async_result_run_in_thread (GSimpleAsyncResult     *simple,
  * _finish function from which this function is called).
  *
  * Returns: #TRUE if all checks passed or #FALSE if any failed.
+ *
+ * Since: 2.20
  **/
 gboolean
 g_simple_async_result_is_valid (GAsyncResult *result,