* net.cc (ga_dup): New function, taken from ga_clone with v4-in-v6

	* net.cc (ga_dup): New function, taken from ga_clone with v4-in-v6
	mapping addition.
	(ga_clone): Just call ga_dup from here.
	(ga_duplist): New function to duplicate list of struct addrinfo.
	(ga_echeck): Don't check a_flags, it already happened in
	cygwin_getaddrinfo.
	(cygwin_freeaddrinfo): Always call ipv4_freeaddrinfo.
	(cygwin_getaddrinfo): Use new wincap.supports_all_posix_ai_flags
	flag rather than wincap.has_gaa_on_link_prefix.  Always duplicate
	WinSock's addrinfo list to a self-allocated list.  Handle AI_V4MAPPED
	for pre-Vista platforms supporting getaddrinfo.
	* wincap.h (wincapc::supports_all_posix_ai_flags): New element.
	* wincap.cc: Implement above element throughout.
	* include/netdb.h: Note how AI_ADDRCONFIG is not supported pre-Vista.
	Remove superfluous comment.