[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_ecommunity.c b/bgpd/bgp_ecommunity.c
index c08673c..27c3cd6 100644
--- a/bgpd/bgp_ecommunity.c
+++ b/bgpd/bgp_ecommunity.c
@@ -673,7 +673,7 @@
 	  eas.val = (*pnt++ << 8);
 	  eas.val |= (*pnt++);
 
-	  len = sprintf( str_buf + str_pnt, "%s%d:%d", prefix,
+	  len = sprintf( str_buf + str_pnt, "%s%u:%d", prefix,
                         eas.as, eas.val );
 	  str_pnt += len;
 	  first = 0;
@@ -688,7 +688,7 @@
 	  eas.val |= (*pnt++ << 8);
 	  eas.val |= (*pnt++);
 
-	  len = sprintf (str_buf + str_pnt, "%s%d:%d", prefix,
+	  len = sprintf (str_buf + str_pnt, "%s%u:%d", prefix,
 			 eas.as, eas.val);
 	  str_pnt += len;
 	  first = 0;