Fix the MSDOS build.

Fix the MSDOS build.

 src/unexcoff.c [MSDOS]: Include libc/atexit.h.
 (copy_text_and_data): Zero out the atexit chain pointer before
 dumping Emacs.
 src/termhooks.h (encode_terminal_code): Update prototype.
 src/term.c (encode_terminal_code) [DOS_NT]: Make it externally
 visible for all DOS_NT ports, not just WINDOWSNT.
 (syms_of_term) [!MSDOS]: Don't define 'tty-menu-*' symbols on MSDOS.
 src/sysdep.c (emacs_sigaction_init, init_signals): Don't use SIGCHLD
 unless it is defined.
 (emacs_pipe) [MSDOS]: Redirect to 'pipe'.
 src/process.c (close_on_exec, accept4, process_socket): Move into
 the "ifdef subprocesses" part.
 (catch_child_signal): Condition by "ifdef subprocesses".
 (syms_of_process) <Qinternal_default_process_sentinel>
 <Qinternal_default_process_filter>: Condition by "ifdef subprocesses".
 src/msdos.h: Add prototypes for new functions.
 (EINPROGRESS): Define.
 (O_CLOEXEC): Define to zero.
 src/msdos.c (check_window_system): Remove unnecessary an
 incompatible duplicate function.
 (sys_opendir, readlinkat, faccessat, fstatat, unsetenv): New
 functions in support of new functionality.
 src/menu.c (single_menu_item): Add visual indication  of submenu
 also for menus on MSDOS frames.
 (Fx_popup_menu) [!MSDOS]: Do not call tty_menu_show on MSDOS.
 src/lisp.h (CHECK_PROCESS) [!subprocesses]: Do not define
 when async subprocesses aren't supported.
 src/font.h (FONT_WIDTH) [MSDOS]: MSDOS-specific definition.
 src/emacs.c (close_output_streams): Zero out errno before calling
 close_stream.
 src/dired.c [MSDOS]: Include msdos.h.
 src/conf_post.h (opendir) [MSDOS]: Redirect to sys_opendir.
 (DATA_START) [MSDOS]: Define.
 (SYSTEM_PURESIZE_EXTRA) [MSDOS]: Enlarge by 25K.
 src/callproc.c (block_child_signal, unblock_child_signal) [MSDOS]:
 Ifdef away for MSDOS.
 (record_kill_process) [MSDOS]: Ifdef away the entire body for MSDOS.
 (call_process_cleanup) [MSDOS]: Ifdef away portions not relevant
 for MSDOS.
 (call_process) [MSDOS]: Fix call sequence of dostounix_filename.
 Use temporary file template that is compatible with mkostemp.
 Move vfork-related portions under #ifndef MSDOS.
 (syms_of_callproc): Unify templates of MSDOS and WINDOWSNT.

 lisp/term/pc-win.el (x-list-fonts, x-get-selection-value): Provide
 doc strings, as required by snarf-documentation.

 msdos/sedlisp.inp:
 msdos/sedlibmk.inp:
 msdos/sedleim.inp:
 msdos/sed3v2.inp:
 msdos/sed2v2.inp:
 msdos/sed1v2.inp: Update Sed scripts for Emacs 24.4.
 msdos/inttypes.h: Add PRIdMAX.
 msdos/INSTALL: Update for Emacs 24.4.
 msdos/sedadmin.inp: New file.