Please describe the problem:
The selection list which is given to extensions is wrong when two selected files
have
the same MIME type. Files are missing in this list : there is at most one file
in the list per
MIME type.

Steps to reproduce:
Install nautilus-actions 0.4.alpha from
http://www.grumz.net/irc/nautilus-actions-0.4.alpha.tar.gz,
put nautilus-actions-0.4.alpha/config/config_gvimdiff.xml in
~/.nautilus-actions, edit it to replace /home/grumz with your home directory,
put nautilus-actions-0.4.alpha/config/show_param.sh in ~/bin, restart Nautilus.

(Yeah it's not very easy ; that's not my software either :-)

Select two files which do not have the same MIME type. Right-click, Diff with
Gvim. Do the same thing with two files that have the same MIME type. 

Actual results:
When both files have the same MIME type it shows nothing. There is only ONE
element in the list which is passed to the extension, so it can't diff.

When both files don't have the same MIME type, it shows something. There was TWO
elements in the list.

Expected results:
To work whatever the MIME types are.

Does this happen every time?
For sure.

Other information:
Tracing into nautilus isn't very funny.

In fact the problem happens in src/file-manager/fm-directory-view.c, in
reset_extension_actions_menu(), after get_unique_files() has been called on the
selection list.

get_unique_files() uses has_file_in_list() to determine if a file is already
present in a list, but this function is totally broken : it compares the MIME
types of files !

The solution is to compare URIs. Here is the old implementation :

gboolean
has_file_in_list (GList *list, NautilusFile *file)
{
        gboolean ret = FALSE;
        char *mime;
       
        mime = nautilus_file_get_mime_type (file);
        
        for (; list; list = list->next) {
                NautilusFile *tmp_file = list->data;
                char *tmp_mime = nautilus_file_get_mime_type (tmp_file);

                if (strcmp (tmp_mime, mime) == 0) {
                        ret = TRUE;
                        g_free (tmp_mime);
                        break;
                }

                g_free (tmp_mime);
        }
        
        g_free (mime);
        return ret;
}

And here is what I propose :
static gboolean
has_file_in_list (GList *list, NautilusFile *file)
{
        gboolean ret = FALSE;
        char *uri;
       
        uri = nautilus_file_get_uri (file);
        
        for (; list; list = list->next) {
                NautilusFile *tmp_file = list->data;
                char *tmp_uri = nautilus_file_get_uri (tmp_file);

                if (strcmp (tmp_uri, uri) == 0) {
                        ret = TRUE;
                        g_free (tmp_uri);
                        break;
                }

                g_free (tmp_uri);
        }
        
        g_free (uri);
        return ret;
}