Treat batch stdout/stderr like standard display

Treat batch stdout/stderr like standard display

Calls like (print FOO) could generate improperly encoded or
hard-to-read output if FOO contains characters outside the system
locale.  Fix this by treating batch stdout and stderr like
interactive standard display, when it comes to transliterating and
encoding characters (Bug#20545).
* doc/emacs/mule.texi (Communication Coding):
* doc/lispref/display.texi (Active Display Table):
* doc/lispref/nonascii.texi (Locales):
* etc/NEWS:
* src/coding.c (syms_of_coding):
* src/dispnew.c (syms_of_display):
Document this.
* src/print.c: Include disptab.h.
(printchar_to_stream): New function, with much of the guts of the
old Fexternal_debugging_output, except this one also uses the
standard display table.
(printchar, strout, Fexternal_debugging_output): Use it.