* modified the directx video plugin to try to create an YUV surface before
   falling back to an RGB surface when it's not possible to use overlays.
   Some graphic cards can do the YUV->RGB conversion in hardware during the
   blitting stage.
* in the directx video plugin, we now request that the RGB surface be created
   in video memory. The reasoning behind this is that usually surfaces in
   video memory benefit from more hardware acceleration (like for instance
   hw rescaling, hw blitting, etc...)
* added two options to the directx video plugin to disable the above features.
   (mainly because my video driver is buggy and doesn't handle them well).

* small cosmetic changes to the generation of the config file.

* fix for config_GetHomeDir() on win32. SHGetFolderPath() is located in
   shfolder.dll not shell32.dll.
* fix for the gtk preferences dialog box. To be sure that an int or float value
   is actually changed we call gtk_spin_button_update() in the
   GtkInt/FloatChanged() event handler.