Fix drag-and-drop of files with multibyte filenames

Fix drag-and-drop of files with multibyte filenames

* lisp/dired.el (dired-mouse-drag): Fix re-signalling of errors.

* lisp/select.el (xselect-convert-to-filename):
(xselect-convert-to-text-uri-list):
(xselect-convert-to-dt-netfile): Encode in raw-text-unix.

* src/xgselect.c (suppress_xg_select, release_xg_select): New
functions.
(xg_select): Respect xg_select suppression by delegating to
pselect.
* src/xgselect.h: Update prototypes.

* src/xterm.c (x_dnd_begin_drag_and_drop): Suppress xg_select
during the nested event loop.
(handle_one_xevent): Handle cases where hold_quit is nil inside
a selection event handler during DND.