Use emacs_open more consistently when opening files.

Use emacs_open more consistently when opening files.

This handles EINTR more consistently now, and makes it easier
to introduce other uniform changes to file descriptor handling.
* src/systdio.h: New file.
* src/buffer.c (mmap_init):
* cygw32.c (chdir_to_default_directory):
* dispnew.c (Fopen_termscript):
* emacs.c (Fdaemon_initialized):
* fileio.c (Fdo_auto_save):
* image.c (slurp_file, png_load_body, jpeg_load_body):
* keyboard.c (Fopen_dribble_file):
* lread.c (Fload):
* print.c (Fredirect_debugging_output):
* sysdep.c (get_up_time, procfs_ttyname, procfs_get_total_memory):
* termcap.c (tgetent):
* unexaix.c, unexcoff.c (unexec, adjust_lnnoptrs):
* unexcw.c, unexelf.c, unexhp9k800.c, unexmacosx.c (unexec):
* w32term.c (w32_initialize) [CYGWIN]:
* xfaces.c (Fx_load_color_file):
Use emacs_open instead of plain open, and emacs_fopen instead of
plain fopen.
* dispnew.c, fileio.c, image.c, keyboard.c, lread.c, print.c, sysdep.c:
* xfaces.c: Include sysstdio.h rather than stdio.h, for emacs_fopen.
* callproc.c (default_output_mode): New constant.
(Fcall_process): Use it to call emacs_open instead of plain creat.
* dispnew.c (Fopen_termscript): Fix minor race in opening termscript.
* sysdep.c (emacs_open): Add commentary and don't call file name "path".
(emacs_fopen): New function.
* unexaix.c, unexcoff.c, unexelf.c, unexhp9k800.c, unexmacosx.c:
Include <lisp.h>, for emacs_open.
* unexelf.c (fatal): Remove decl; not needed with <lisp.h> included.