Allow GdkPixbufSimpleAnim to loop

Add a GdkPixbufSimpleAnim:loop boolean property and its accessors.
Based on a patch by Tim Evans. (#561139)

docs/reference/gdk-pixbuf/gdk-pixbuf-sections.txt

@@ -136,6 +136,8 @@ gdk_pixbuf_animation_iter_get_pixbuf
 GdkPixbufSimpleAnim
 gdk_pixbuf_simple_anim_new
 gdk_pixbuf_simple_anim_add_frame
+gdk_pixbuf_simple_anim_set_loop
+gdk_pixbuf_simple_anim_get_loop
 
 <SUBSECTION Standard>
 GDK_PIXBUF_ANIMATION

docs/reference/gdk-pixbuf/tmpl/animation.sgml

@@ -172,3 +172,21 @@ An opaque struct representing a simple animation.
 @pixbuf: 
 
 
+<!-- ##### FUNCTION gdk_pixbuf_simple_anim_set_loop ##### -->
+<para>
+
+</para>
+
+@animation: 
+@loop: 
+
+
+<!-- ##### FUNCTION gdk_pixbuf_simple_anim_get_loop ##### -->
+<para>
+
+</para>
+
+@animation: 
+@Returns: 
+
+