`write-region-inhibit-fsync' defaults to noninteractive.

`write-region-inhibit-fsync' defaults to noninteractive.

* cmdargs.texi (Initial Options):
* files.texi (Customize Save): Document this.
* etc/NEWS: Document this.
* src/fileio.c (syms_of_fileio): Implement this.
* src/filelock.c (create_lock_file): If symbolic links don't work, so
we use a regular file as a lock file, do not fsync the lock file;
it's not needed.