[bgpd] AS4 bugfix by Chris Caputo <ccaputo@alt.net>

* bgpd/bgp_aspath.c: (aspath_make_str_count) "assert (len < str_size)" was
  getting hit under certain 4-byte ASN conditions. New realloc strategy.
* bgpd/bgp_aspath.c: (aspath_key_make) const warning fix.

"%d" -> "%u" 4-byte ASN corrections.  Prevent negative number when ASN is
above 2^31.
diff --git a/bgpd/bgp_debug.c b/bgpd/bgp_debug.c
index 757b9cf..1d5bf6b 100644
--- a/bgpd/bgp_debug.c
+++ b/bgpd/bgp_debug.c
@@ -205,7 +205,7 @@
     snprintf (buf + strlen (buf), size - strlen (buf), ", atomic-aggregate");
 
   if (CHECK_FLAG (attr->flag, ATTR_FLAG_BIT (BGP_ATTR_AGGREGATOR)))
-    snprintf (buf + strlen (buf), size - strlen (buf), ", aggregated by %d %s",
+    snprintf (buf + strlen (buf), size - strlen (buf), ", aggregated by %u %s",
 	      attr->extra->aggregator_as,
 	      inet_ntoa (attr->extra->aggregator_addr));