Support file name dialog on NS.

Support file name dialog on NS.

* etc/NEWS: Mention that the file dialog is used on NS.

* lisp/term/ns-win.el (x-file-dialog): New function.

* src/fileio.c (Fnext_read_file_uses_dialog_p): Add HAVE_NS.

* src/nsfns.m (ns_frame_parm_handlers): Add x_set_fullscreen.

* src/nsfns.m (Fns_read_file_name): Add argument DIR_ONLY_P.
Initialize panel name field if OSX >= 10.6.

* src/w32fns.c (Fx_file_dialog): Update comment.

* src/xfns.c (Fx_file_dialog): Update comment.