Description of problem
   ############################
   The "File Management Preferences" dialog has some issues
     * It still use the (deprecated) GtkOptionMenu widget
     * The "Icon Captions" tab don't follow the HIG specs

     * "Label  the  drop-down  list  with a text label above it or to its
       left"
     * explanatory text in dialog
     * Global  options  are mixed with specific view options, for example
       list view options appears in both "Views" and "List Columns" tabs

   So I picked up my glade and I tried to build up something.

   Actual results
   ############################

   Here a detailed list of changes (items starting for '>' means just for
   fun, not implementable actually :-)

   General
     * dialog spacings
     * renamed tabs labels


   Displaying
     * removed  hbox11 (containing default_view_optionmenu): HIG said "Do
       not use drop-down lists with fewer than three items".
     * s/sort_order_optionmenu/sort_order_combobox
     * note that sort_order_optionmenu use bad capitalization
     * add a "Manually" sorting option in sort_order_combobox
     * removed  the "Tree View Defaults": now we are spatial, we can keep
       it simply as a GConf key, don't expose in UI
     * moved list and icon view specific controls in appropriate tab
     * use radio controls to choose default view
     * > add a detailed (MacOSX Finder style) selection on showed volumes
       on Desktop [1]

   Management
     * add a couple of radio (spatial_radiobutton and
       browser_radiobutton) to connect to
       /apps/nautilus/preferences/always_use_browser GConf key
     * Use  the  "Behavior"  section  to  set spatial/browser UI. Use the
       "Items Activation" to set click policy.
     * delete the "Executable Text Files" section and pack it as dropdown
       list (scripts_combobox) in "Item Activation" section

   Icon View
     * s/iconview_zoom_optionmenu/iconview_zoom_combobox
     * add    labels    (not    so    good   but   HIG   compliant)   for
       captions_*_optionmenu and convert them to ComboBox

   List View
     * s/listview_zoom_optionmenu/listview_zoom_combobox

   Preview
     * s/optionmenu/combobox

   [1]  we  have already the /apps/nautilus/desktop/volumes_visible GConf
   key, but it's a TRUE/FALSE for ALL volumes (hard, removable, server).
   [2]  if  and when someone will implement it, IMHO we don't need to add
   it as a third view.