Fix typo.
net.address2() was extensively reworked.

But it was marked experimental, so it's okay.  It can change.
Fix error handling for getaddrinfo()

Of course getaddrinfo() returns its own error messages.  So I created a
table in net called errno, which lists the errors.  Also, net.address2()
returns not one, but *two* different error numbers, the one from
getaddrinfo() and errno.  Use errno only if the getaddrinfo() return value
is EAI_SYSTEM.