tinc 1.1: freeaddrinfo(NULL) crash on windows

[Todd C. Miller]

Unfortunately, my fix exposed a problem in reset_address_cache()
could call free_known_addresses() on a struct addrinfo * that was
returned by getaddrinfo().  This results in heap corruption on
Windows (and a crash).

It seems safest to just make a copy of the addresses returned by
getaddrinfo() so it can always use free_known_addresses() instead
of trying to determine whether or not we need to use freeaddrinfo().

https://github.com/gsliepen/tinc/pull/178

 - todd