Implement memset_s() and use it instead of zero_bytes().

A new constant, SUDO_CONV_REPL_MAX, is defined by the plugin
API as the max conversation reply length.  This constant can be
used as a max value for memset_s() when clearing passwords
filled in by the conversation function.

plugins/sudoers/sudoers.c

@@ -807,7 +807,7 @@ set_fqdn(void)
     char *p;
     debug_decl(set_fqdn, SUDO_DEBUG_PLUGIN)
 
-    zero_bytes(&hint, sizeof(hint));
+    memset(&hint, 0, sizeof(hint));
     hint.ai_family = PF_UNSPEC;
     hint.ai_flags = AI_FQDN;
     if (getaddrinfo(user_host, NULL, &hint, &res0) != 0) {