* environ.cc (set_winsymlinks): Handle "winsymlinks:nativestrict"
	option.  On pre-Vista warn the user if the "winsymlinks:native*" option
	is set.
	* globals.cc (enum winsym_t): Add WSYM_nativestrict.
	* path.cc (symlink_native): Don't create native symlink if target
	does not exist.  Explain why.  Improve comments.
	(symlink_worker): Change AFS symlink handling to WSYM_nativestrict.
	Handle WSYM_nativestrict throughout.  Change condition for bail out
	to wsym_type == WSYM_nativestrict.  Add comment.  Fix formatting.
	* shared_info.h (CURR_USER_MAGIC): Change to reflect change in
	class user_info.
	(class user_info): Add member warned_nonativesyms.
	* cygwinenv.xml (cygwinenv-implemented-options): Explain new
	winsymliks:nativestrict option.  Strip out description of symlink types
	and refer to new pathnames-symlinks section.
	* highlights.xml (ov-hi-files): Rip out most of symlink description and
	refer to new pathnames-symlinks section instead.
	* new-features.xml (ov-new1.7.19): Add CYGWIN=winsymlinks:nativestrict.
	* pathnames.xml (pathnames-symlinks): New section describing symbolic
	link handling.
	* libc/ctype/isalnum.c: Correct domain of definition to SUSv4 wording.
	* libc/ctype/isalpha.c: Ditto.
	* libc/ctype/isblank.c: Ditto.
	* libc/ctype/iscntrl.c: Ditto.
	* libc/ctype/isdigit.c: Ditto.
	* libc/ctype/islower.c: Ditto.
	* libc/ctype/isprint.c: Ditto.
	* libc/ctype/ispunct.c: Ditto.
	* libc/ctype/isxdigit.c: Ditto.