MEDIUM: log: Unique ID

The Unique ID, is an ID generated with several informations. You can use
a log-format string to customize it, with the "unique-id-format" keyword,
and insert it in the request header, with the "unique-id-header" keyword.
diff --git a/include/proto/log.h b/include/proto/log.h
index 0e41eca..5adf674 100644
--- a/include/proto/log.h
+++ b/include/proto/log.h
@@ -33,6 +33,7 @@
 #include <types/session.h>
 
 extern struct pool_head *pool2_requri;
+extern struct pool_head *pool2_uniqueid;
 
 extern char *log_format;
 extern char default_tcp_log_format[];