[MEDIUM] buffers: add BF_READ_ATTACHED and BF_ANA_TIMEOUT

Those two flags will be used to wake up analysers only when
needed.
diff --git a/src/client.c b/src/client.c
index aed9415..953e41e 100644
--- a/src/client.c
+++ b/src/client.c
@@ -342,6 +342,8 @@
 		s->req->cons = &s->si[1];
 		s->si[0].ib = s->si[1].ob = s->req;
 
+		s->req->flags |= BF_READ_ATTACHED; /* the producer is already connected */
+
 		if (p->mode == PR_MODE_HTTP) /* reserve some space for header rewriting */
 			s->req->rlim -= MAXREWRITE;