Add correct variable names for _POSIX_IPV6 and _POSIX_RAW_SOCKETS

getconf only recognizes IPV6 and RAW_SOCKETS, when the standard
requires it to recognize the actual configuration variable name[1].  I
have not removed the earlier names for compatibility.

	* posix/getconf.c (vars): Add _POSIX_IPV6 and
	_POSIX_RAW_SOCKETS.

[1] http://pubs.opengroup.org/onlinepubs/007904875/functions/sysconf.html
Remove _POSIX_REGEX_VERSION

There is no _POSIX_REGEX_VERSION, so don't check for it.
_REGEX_VERSION has been removed as well[1], so only keep the -1 return
for backward compatibility.  I found this when trying to make the
getconf environment variables typo-proof.

	* sysdeps/posix/sysconf.c (__sysconf): Return -1 for
	_SC_REGEX_VERSION.

[1] http://pubs.opengroup.org/onlinepubs/009695399/functions/sysconf.html
Handle zero prefix length in getifaddrs (BZ #17371)