[gtk+] gtkdnd: Fix introspection annotations in some functions

[Carlos Garnacho <carlosg src gnome org>]

commit 9e2092d3063744dde05827b5d42442bb82c00796
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Jul 7 12:50:14 2015 +0200

    gtkdnd: Fix introspection annotations in some functions
    
    The GdkEvent field is nullable on gtk_drag_begin*, and gtk_drag_cancel()
    is a method, like the rest of the DnD API.

 gtk/gtkdnd.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkdnd.c b/gtk/gtkdnd.c
index 399e319..2978568 100644
--- a/gtk/gtkdnd.c
+++ b/gtk/gtkdnd.c
@@ -2582,7 +2582,8 @@ gtk_drag_begin_internal (GtkWidget         *widget,
  *    source can provide the data
  * @actions: A bitmask of the allowed drag actions for this drag
  * @button: The button the user clicked to start the drag
- * @event: The event that triggered the start of the drag
+ * @event: (nullable): The event that triggered the start of the drag,
+ *    or %NULL if none can be obtained.
  * @x: The initial x coordinate to start dragging from, in the coordinate space
  *    of @widget. If -1 is passed, the coordinates are retrieved from @event or
  *    the current pointer position
@@ -2644,7 +2645,8 @@ gtk_drag_begin_with_coordinates (GtkWidget     *widget,
  *    source can provide the data
  * @actions: A bitmask of the allowed drag actions for this drag
  * @button: The button the user clicked to start the drag
- * @event: The event that triggered the start of the drag
+ * @event: (nullable): The event that triggered the start of the drag,
+ *    or %NULL if none can be obtained.
  *
  * This function is equivalent to gtk_drag_begin_with_coordinates(),
  * passing -1, -1 as coordinates.
@@ -4386,7 +4388,7 @@ gtk_drag_check_threshold (GtkWidget *widget,
 }
 
 /**
- * gtk_drag_cancel:
+ * gtk_drag_cancel: (method)
  * @context: a #GdkDragContext, as e.g. returned by gtk_drag_begin_with_coordinates()
  *
  * Cancels an ongoing drag operation on the source side.