[gimp] app: make --show-playground visible in --help.

[Jehan Pagès <jehanp src gnome org>]

commit 4d6cba0cfb0e7408d441b8c2537ef6e43788d5a5
Author: Jehan <jehan girinstud io>
Date:   Sat Apr 21 15:48:22 2018 +0200

    app: make --show-playground visible in --help.
    
    After Alexandre Prokoudine's insistent demand! :-)
    I am still not sure how wise this is, since this should be really
    considered a "developer-only" option. Basically these tools are really
    too buggy and unstable and we should not shine too much light on these.
    The counter-argument is that doing so will favor the bitrot.
    
    Well ok. At least let's add a big warning message at the top of the
    Playground page, to make it very clear (if that were not already the
    case) that basically this is not to be considered a secret feature, but
    really more a "we are looking for contributors" option.

 app/dialogs/preferences-dialog.c |   11 +++++++++++
 app/main.c                       |    2 +-
 2 files changed, 12 insertions(+), 1 deletions(-)
---
diff --git a/app/dialogs/preferences-dialog.c b/app/dialogs/preferences-dialog.c
index f061cb5..fe5e5e8 100644
--- a/app/dialogs/preferences-dialog.c
+++ b/app/dialogs/preferences-dialog.c
@@ -1553,6 +1553,17 @@ prefs_dialog_new (Gimp       *gimp,
                                       NULL,
                                       &top_iter);
 
+      hbox = g_object_new (GIMP_TYPE_HINT_BOX,
+                           "icon-name", GIMP_ICON_DIALOG_WARNING,
+                           "hint",      _("These features are unfinished, buggy "
+                                          "and may crash GIMP. It is unadvised to "
+                                          "use them unless you really know what "
+                                          "you are doing or you intend to contribute "
+                                          "patches."),
+                           NULL);
+      gtk_box_pack_start (GTK_BOX (vbox), hbox, FALSE, FALSE, 0);
+      gtk_widget_show (hbox);
+
       vbox2 = prefs_frame_new (_("Insane Options"),
                                GTK_CONTAINER (vbox), TRUE);
 
diff --git a/app/main.c b/app/main.c
index 60e846b..b8515c6 100644
--- a/app/main.c
+++ b/app/main.c
@@ -280,7 +280,7 @@ static const GOptionEntry main_entries[] =
     N_("Output a sorted list of deprecated procedures in the PDB"), NULL
   },
   {
-    "show-playground", 0, G_OPTION_FLAG_HIDDEN,
+    "show-playground", 0, 0,
     G_OPTION_ARG_NONE, &show_playground,
     N_("Show a preferences page with experimental features"), NULL
   },