Fix for CVE-2016-10196

More details at:

  https://github.com/libevent/libevent/issues/318

Based on commit at:

  https://github.com/libevent/libevent/commit/329acc18a0768c21ba22522f01a5c7f46cacc4d5

--- libevent-2.0.22/evutil.c.orig	2017-02-02 07:20:55.460219824 +0000
+++ libevent-2.0.22/evutil.c	2017-02-02 07:25:18.285916416 +0000
@@ -1808,12 +1808,12 @@
 
 	cp = strchr(ip_as_string, ':');
 	if (*ip_as_string == '[') {
-		int len;
+		size_t len;
 		if (!(cp = strchr(ip_as_string, ']'))) {
 			return -1;
 		}
-		len = (int) ( cp-(ip_as_string + 1) );
-		if (len > (int)sizeof(buf)-1) {
+		len = ( cp-(ip_as_string + 1) );
+		if (len > sizeof(buf)-1) {
 			return -1;
 		}
 		memcpy(buf, ip_as_string+1, len);