[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_attr.c b/bgpd/bgp_attr.c
index d116c30..f38db41 100644
--- a/bgpd/bgp_attr.c
+++ b/bgpd/bgp_attr.c
@@ -857,7 +857,7 @@
 	  && ! aspath_firstas_check (attr->aspath, peer->as))
  	{
  	  zlog (peer->log, LOG_ERR,
- 		"%s incorrect first AS (must be %d)", peer->host, peer->as);
+ 		"%s incorrect first AS (must be %u)", peer->host, peer->as);
  	  bgp_notify_send (peer,
  			   BGP_NOTIFY_UPDATE_ERR,
  			   BGP_NOTIFY_UPDATE_MAL_AS_PATH);