* src/w32term.c (syms_of_w32term) <w32-yes-no-dialog-show-cancel>:
New boolean variable.
(w32_initialize): Fix query for visible system caret: 'bool' is a
single-byte data type, whereas SystemParametersInfo wants a BOOL,
which is a 32-bit int.
* src/w32menu.c (simple_dialog_show): Show "Cancel" button only if
'w32-yes-no-dialog-show-cancel' is non-nil.

* etc/NEWS: Announce the change.

* src/nsterm.m (ns_draw_glyphless_glyph_string_foreground):
* src/pgtkterm.c (pgtk_draw_glyphless_glyph_string_foreground):
* src/haikuterm.c (haiku_draw_glyphless_glyph_string_foreground):
* src/xterm.c (x_draw_glyphless_glyph_string_foreground):
* src/w32term.c (w32_draw_glyphless_glyph_string_foreground):
* src/xdisp.c (lookup_glyphless_char_display): Handle extra-slot
of 'glyphless-char-display' that is a cons cell.
(syms_of_xdisp) <glyphless-char-display>: Update doc string.

* etc/NEWS:
* doc/lispref/display.texi (Glyphless Chars): Document the new
feature.

* lisp/faces.el (glyphless-char): Make the face stand out on TTY
frames that don't support the underline attribute.

Qunbound is uninterned and can therefore never be EQ to any symbol
with position.

* src/buffer.c (Fbuffer_local_value, buffer_lisp_local_variables)
(buffer_local_variables_1):
* src/bytecode.c (exec_byte_code):
* src/comp.c (compile_function, Fcomp__compile_ctxt_to_file):
* src/composite.c (composition_gstring_cache_clear_font):
* src/data.c (Fboundp, Fsymbol_value, set_internal)
(Fdefault_boundp, Fdefault_value, Fmake_variable_buffer_local):
* src/emacs-module.c (module_global_reference_p):
* src/eval.c (Fdefault_toplevel_value, defvar)
(run_hook_with_args):
* src/fns.c (hash_put, Fmaphash):
* src/font.c (font_put_extra):
* src/frame.c (gui_set_frame_parameters)
(gui_frame_get_and_record_arg, gui_default_parameter)
(gui_figure_window_size):
* src/haikufns.c (get_geometry_from_preferences)
(haiku_create_frame, haiku_create_tip_frame):
* src/haikuterm.c (haiku_draw_text_decoration)
(haiku_default_font_parameter):
* src/json.c (lisp_to_json_nonscalar_1):
* src/keymap.c (access_keymap_1, access_keymap, current_minor_maps):
* src/lread.c (readevalloop, define_symbol):
* src/minibuf.c (read_minibuf, Ftry_completion):
(Fall_completions, Ftest_completion):
* src/pgtkfns.c (pgtk_default_font_parameter, Fx_create_frame)
(x_create_tip_frame):
* src/pgtkselect.c (Fpgtk_own_selection_internal):
* src/print.c (print):
* src/profiler.c (evict_lower_half, record_backtrace):
* src/terminal.c (create_terminal):
* src/textprop.c (set_properties):
* src/w32fns.c (my_create_window, w32_icon)
(w32_default_font_parameter, Fx_create_frame)
(w32_create_tip_frame):
* src/w32term.c (w32_draw_glyph_string):
* src/xdisp.c (handle_single_display_spec)
(cursor_row_fully_visible_p, calc_pixel_width_or_height):
* src/xfns.c (x_default_scroll_bar_color_parameter, x_icon_verify)
(x_icon, x_default_font_parameter, Fx_create_frame)
(x_create_tip_frame):
* src/xselect.c (x_handle_selection_request):
* src/xterm.c (x_draw_glyph_string, x_term_init):
Use BASE_EQ instead of EQ when comparing with Qunbound.

* src/w32term.c (w32_read_socket): Handle WM_DISPLAYCHANGE by
sending monitor change events.

* src/w32term.c (w32_read_socket): Fix typo in check before
flipping buffers.

* src/minibuf.c (read_minibuf): Call `w32_flip_buffers_if_dirty'
after changing the cursor position and redisplaying instead of
`flush_frame'.  (bug#55193)

* src/w32term.c (w32_flip_buffers_if_dirty): New function.
* src/w32term.h: Update prototypes.

* src/w32fns.c (w32_set_inhibit_double_buffering): Add comment
describing double buffering.
(w32_wnd_proc): Respect `w32-disable-double-buffering'.
(globals_of_w32fns): New variable
`w32-disable-double-buffering'.

* src/w32term.c (w32_show_back_buffer): Return immediately if
double buffering is disabled on the frame.
(w32_scroll_run): Use old scrolling code if
`w32-disable-double-buffering' is enabled.
(w32_scroll_bar_clear): Document why we don't clear scroll bars
when double buffering is enabled.
(w32_read_socket): Respect `w32-disable-double-buffering' and
clean up some code.

* src/w32xfns.c (get_frame_dc): Respect
`w32-disable-double-buffering'.