* libc/time/strftime.c: Adapt for dual-purpose use so not only

	* libc/time/strftime.c:  Adapt for dual-purpose use so not only
	defines strftime(), but can also define wcsftime(); add optional
	test package; speed up %Y handling.
	* libc/time/wcsftime.c:  New file, defining wcsftime() (albeit
	indirectly by including strftime.c) and its documentation.
	* libc/time/time.tex:  Enhance tm_isdst explanation, change strftime
	description to match modified description in strftime.c
	* libc/time/Makefile.am:  Add wcsftime.c and wcsftime.def.  Add a rule
	so that wcsftime.o gets rebuilt when strftime changes.
	* libc/time/Makefile.in:  Regenerate.
	* libc/include/wchar.h (wcsftime): Declare.