Add two implementations of getaddrinfo: one blocking and one nonblocking. The entry points are evutil_getaddrinfo and evdns_getaddrinfo respectively. There are fairly extensive unit tests. I believe this code conforms to RFC3493 pretty closely, but there are probably more issues. It should get tested on more platforms. This code means we can dump the well-intentioned but weirdly-implemented bufferevent_evdns and evutil_resolve code. svn:r1537