* libc/include/wchar.h (mbsnrtowcs): Declare.

	* libc/include/wchar.h (mbsnrtowcs): Declare.
	(_mbsnrtowcs_r): Declare.
	(wcsnrtombs): Declare.
	(_wcsnrtombs_r): Declare.
	* libc/stdlib/Makefile.am (ELIX_2_SOURCES): Add mbsnrtowcs.c
	and wcsnrtombs.c.
	* libc/stdlib/Makefile.in: Regenerate.
	* libc/stdlib/mbsnrtowcs.c: New file, implementing _mbsnrtowcs_r
	and mbsnrtowcs.  Document mbsnrtowcs and mbsrtowcs.
	* libc/stdlib/mbsrtowcs.c (_mbsrtowcs_r): Just call _mbsnrtowcs_r.
	(mbsrtowcs): Ditto.
	* libc/stdlib/wcsnrtombs.c: New file, implementing _wcsnrtombs_r
	and wcsnrtombs.  Document wcsrtombs and wcsnrtombs.
	* libc/stdlib/wcsrtombs.c (_wcsrtombs_r): Just call _wcsnrtombs_r.
	(wcsrtombs): Ditto.
	* libc/stdlib/stdlib.tex: Accommodate new documentation.