BUG/MEDIUM: stream: Don't forget to free s->unique_id in stream_free().

In stream_free(), free s->unique_id. We may still have one, because it's
allocated in log.c::strm_log() no matter what, even if it's a TCP connection
and thus it won't get free'd by http_end_txn().
Failure to do so leads to a memory leak.

This should probably be backported to all maintained branches.
diff --git a/src/stream.c b/src/stream.c
index 939c4db..a96ddcb 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -386,6 +386,8 @@
 		offer_buffers(NULL, tasks_run_queue);
 	}
 
+	pool_free(pool_head_uniqueid, s->unique_id);
+
 	hlua_ctx_destroy(s->hlua);
 	s->hlua = NULL;
 	if (s->txn)