actions: Merge floating selection with Select None

In Paintshop Pro, you can merge floating selections
down with Select None.
This patch adds that same functionality to GIMP.

app/actions/select-actions.c

@@ -186,7 +186,7 @@ select_actions_update (GimpActionGroup *group,
         gimp_action_group_set_action_sensitive (group, action, (condition) != 0, NULL)
 
   SET_SENSITIVE ("select-all",    image && ! sel_all);
-  SET_SENSITIVE ("select-none",   image && sel);
+  SET_SENSITIVE ("select-none",   image && (sel || fs));
   SET_SENSITIVE ("select-invert", image);
 
   SET_SENSITIVE ("select-cut-float",  g_list_length (drawables) == 1 && sel                 &&

app/actions/select-commands.c

@@ -30,6 +30,7 @@
 
 #include "core/gimp.h"
 #include "core/gimpchannel.h"
+#include "core/gimplayer-floating-selection.h"
 #include "core/gimpimage.h"
 #include "core/gimpselection.h"
 
@@ -97,6 +98,11 @@ select_none_cmd_callback (GimpAction *action,
   return_if_no_image (image, data);
 
   gimp_channel_clear (gimp_image_get_mask (image), NULL, TRUE);
+
+  /* Commit floating selection (if any) */
+  if (gimp_image_get_floating_selection (image))
+    floating_sel_anchor (gimp_image_get_floating_selection (image));
+
   gimp_image_flush (image);
 }