GtkFileSystem::insert_bookmarks change

[Federico Mena Quintero <federico ximian com>]

Hi, Hans, Tor,

I made a little change to the ::add_bookmark() method in GtkFileSystem. 
It is now called differently and adds an extra argument, to wit:

  gboolean (*insert_bookmark) (GtkFileSystem     *file_system,
			       const GtkFilePath *path,
			       gint               position,
			       GError           **error);

I'm adding support for reordering the bookmarks list with drag-and-drop,
so I need that change.

I also noticed that the Win32 implementation of bookmarks doesn't
perform notification when the bookmarks list actually changes --- you
need to do this if the actual insert_bookmark or remove_bookmark
operations succeed; this way the file chooser implementation will know
when to re-read/redraw the bookmarks list.

[Also, isn't the idea to use the Win32 native bookmarks mechanism?  Does
the GtkFileSystem API with its insert_bookmark(fs, pathname, position)
and remove_bookmark(fs, pathname) let you do this easily?  I'm asking
about this because the API freeze is next Monday, so if this API doesn't
accomodate Win32 very well, we need to change it before that...]

  Federico