lread.c, macros.c, marker.c, menu.c, minibuf.c: Use bool for booleans.

lread.c, macros.c, marker.c, menu.c, minibuf.c: Use bool for booleans.

* lread.c (load_each_byte, new_backquote_flag, readchar)
(read_filtered_event, lisp_file_lexically_bound_p)
(safe_to_load_version, Fload, complete_filename_p, openp)
(build_load_history, readevalloop, read_escape, read1)
(string_to_number, read_vector, read_list):
* macros.c (Fstart_kbd_macro):
* marker.c (CONSIDER):
* menu.c (parse_single_submenu, digest_single_submenu)
(find_and_return_menu_selection, Fx_popup_menu):
* minibuf.c (read_minibuf_noninteractive, read_minibuf)
(Ftry_completion):
* nsmenu.m (ns_update_menubar, runMenuAt:forFrame:keymaps:):
(ns_menu_show):
* xmenu.c (set_frame_menubar, create_and_show_popup_menu)
(xmenu_show, xdialog_show):
Use bool for booleans.
* lread.c (safe_to_load_version): Rename from safe_to_load_p,
as it's not a predicate.  All uses changed.  Omit unnecessary
buffer termination.