* fileio.c (Fread_file_name): Pass Qt as fifth parameter to

* fileio.c (Fread_file_name): Pass Qt as fifth parameter to
Fx_file_dialog if only directories should be read.

* lisp.h: Fx_file_dialog takes 5 parameters.

* xfns.c (Fx_file_dialog): Both Motif and GTK version:  Add
parameter only_dir_p.
In Motif version, don't put DEFAULT_FILENAME in filter part of the
dialog, just text field part.  Do not add DEFAULT_FILENAME
to list of files if it isn't there.
In GTK version, pass only_dir_p parameter to xg_get_file_name.

* macfns.c (Fx_file_dialog): Add parameter only_dir_p.  Check
only_dir_p instead of comparing prompt to "Dired".  When using
a save dialog, add option kNavDontConfirmReplacement, change title
to "Enter name", change text for save button to "Ok".

* w32fns.c (Fx_file_dialog): Add parameter only_dir_p.  Check
only_dir_p instead of comparing prompt to "Dired".

* gtkutil.c (xg_get_file_with_chooser)
(xg_get_file_with_selection): New functions, only defined ifdef
HAVE_GTK_FILE_CHOOSER_DIALOG_NEW and HAVE_GTK_FILE_SELECTION_NEW
respectively.
(xg_get_file_name): Add parameter only_dir_p.
Call xg_get_file_with_chooser or xg_get_file_with_selection
depending on HAVE_GTK_FILE* and the value of use_old_gtk_file_dialog.
(xg_initialize): New DEFVAR_BOOL use_old_gtk_file_dialog.

* gtkutil.h (xg_get_file_name): Add parameter only_dir_p.