Convert to libevent.

This is a quick initial conversion that doesn't yet show much advantage:
- We roll our own timeouts.
- We roll our own signal handling.
- We build up the meta connection fd events on each loop rather than
  on state changes.

src/tincd.c

@@ -462,6 +462,11 @@ int main(int argc, char **argv)
 	if(!read_server_config())
 		return 1;
 
+	if(event_init() < 0) {
+		logger(LOG_ERR, _("Error initializing libevent!"));
+		return 1;
+	}
+
 	if(lzo_init() != LZO_E_OK) {
 		logger(LOG_ERR, _("Error initializing LZO compressor!"));
 		return 1;