Fix various little bugs and loosen up various warnings

Change-Id: Iead48ac030290290c7c448b6f72a31380c2e8326
diff --git a/third_party/libevent/evdns.c b/third_party/libevent/evdns.c
index 60b1048..3ae5d8b 100644
--- a/third_party/libevent/evdns.c
+++ b/third_party/libevent/evdns.c
@@ -2471,7 +2471,7 @@
 	ASSERT_LOCKED(base);
 	if (server) {
 		do {
-			if (!evutil_sockaddr_cmp((struct sockaddr*)&server->address, address, 1)) return 3;
+			if (!evutil_sockaddr_cmp((const struct sockaddr*)&server->address, address, 1)) return 3;
 			server = server->next;
 		} while (server != started_at);
 	}