[Usability] Spacing between dialog action area and content widget

[Christian Neumair <chris gnome-de org>]

I've encountered an evil inconsistency that isn't covered by the HIG:
According to the HIG, message dialogs ought to have 24 pixels between
the button action area and the content widget. Other dialogs aren't
covered by the HIG at all when it comes to action area<->content widget
spacing, resulting in property dialogs having 12 pixels and
GtkFileChooserDialog having 24 pixels between them, just like message
dialogs. I don't know what type it has HIG-wise, but I assume it's
neither a message nor a property dialog, instead maybe a
picker/chooser/selector dialog that should be covered by an own section.
Any ideas? How could we resolve this issue? Is it useful to use the same
spacing for all dialogs?

regs,
 Chris