(QUTF8_STRING): New variable.

(QUTF8_STRING): New variable.
(symbol_to_x_atom): Pay attention to QUTF8_STRING.
(x_atom_to_symbol): Likewise.
(x_get_local_selection): New argument local_request.  If it is
nonzero, call handler_fn with the second arg nil.
(x_handle_selection_request): Call x_get_local_selection with
local_request 0.
(lisp_data_to_selection_data): Don't encode the string here.
(Fx_get_selection_internal): Call x_get_local_selection with
local_request 1.
(syms_of_xselect): Intern and staticpro QUTF8_STRING.