* sysdeps/mach/hurd/bind.c: Translate EEXIST from dir_link into
EADDRINUSE. If translated node doesn't grok ifsock protocol,
return EADDRINUSE.
* sysdeps/mach/hurd/connect.c: Make address arg
`const struct sockaddr_un *'.
The redecl is kosher and avoids another variable for AF_LOCAL case.
* sysdeps/mach/hurd/sendto.c: Likewise.
* sysdeps/mach/hurd/bind.c: Likewise.
* socket/sys/socket.h (__SOCKADDR_ARG): Enable transparent_union
code for GCC >= 2.7; use __transparent_union__ for name safety;
add several sockaddr flavors.
(__SOCKADDR_ALLTYPES, __SOCKADDR_ONETYPE): New macros used in
constructing the transparent union declarations.
(__CONST_SOCKADDR_ARG): New type (or macro if not GCC 2.7).
(bind, connect, sendto): Make the sockaddr argument use that.
