a pointer to async-dns alternatives.

apparently glibc 2.2.4 and windows both have async gethostbynames now.
we'll want to make use of them if they're available (via autoconf).


svn:r347

src/or/dns.c

@@ -2,6 +2,11 @@
 /* See LICENSE for licensing information */
 /* $Id$ */
 
+/* See http://elvin.dstc.com/ListArchive/elvin-dev/archive/2001/09/msg00027.html
+ * for some approaches to asynchronous dns. We will want to switch once one of
+ * them becomes more commonly available.
+ */
+
 #include "or.h"
 #include "tree.h"