Add frame type for attached modal dialogs

Add a new frame type META_FRAME_TYPE_ATTACHED which is used for
attached modal dialogs.

The theme format version is bumped to 3.2, and attached windows
can have borders defined in a metacity-theme-3.xml as:

 <window version=">= 3.2" type="attached" style_set="[name]"/>

If no style is defined for "attached", drawing will fall back
to the "border" type.

https://bugzilla.gnome.org/show_bug.cgi?id=592382

src/ui/theme-viewer.c

@@ -407,6 +407,10 @@ get_window_contents (MetaFrameType  type,
     case META_FRAME_TYPE_BORDER:
       *title = _("Border");
       return border_only_contents ();
+
+    case META_FRAME_TYPE_ATTACHED:
+      *title = _("Attached Modal Dialog");
+      return dialog_contents ();
       
     case META_FRAME_TYPE_LAST:
       g_assert_not_reached ();
@@ -454,6 +458,9 @@ get_window_flags (MetaFrameType type)
 
     case META_FRAME_TYPE_BORDER:
       break;
+
+    case META_FRAME_TYPE_ATTACHED:
+      break;
       
     case META_FRAME_TYPE_LAST:
       g_assert_not_reached ();