This allows you to use the samba style @netgroup names in hosts allow
and hosts deny.

This patch still needs autoconf support for portability.

To use this patch, run these commands for a successful build:

    patch -p1 <patches/netgroup-auth.diff
    ./configure                           (optional if already run)
    make

based-on: a01e3b490eb36ccf9e704840e1b6683dab867550
diff --git a/access.c b/access.c
--- a/access.c
+++ b/access.c
@@ -19,11 +19,14 @@
  */
 
 #include "rsync.h"
+#include <netdb.h>
 
 static int match_hostname(const char *host, const char *tok)
 {
 	if (!host || !*host)
 		return 0;
+	if (*tok == '@' && tok[1])
+		return innetgr(tok + 1, host, NULL, NULL);
 	return iwildmatch(tok, host);
 }