MAJOR: buffer: replace buf->l with buf->{o+i}

We don't have buf->l anymore. We have buf->i for pending data and
the total length is retrieved by adding buf->o. Some computation
already become simpler.

Despite extreme care, bugs are not excluded.

It's worth noting that msg->err_pos as set by HTTP request/response
analysers becomes relative to pending data and not to the beginning
of the buffer. This has not been completed yet so differences might
occur when outgoing data are left in the buffer.
diff --git a/src/dumpstats.c b/src/dumpstats.c
index 907e2fe..26cbdd6 100644
--- a/src/dumpstats.c
+++ b/src/dumpstats.c
@@ -1540,9 +1540,9 @@
 	si->ob->wex = TICK_ETERNITY;
 
  out:
-	DPRINTF(stderr, "%s@%d: st=%d, rqf=%x, rpf=%x, rql=%d, rqs=%d, rl=%d, rs=%d\n",
+	DPRINTF(stderr, "%s@%d: st=%d, rqf=%x, rpf=%x, rqh=%d, rqs=%d, rh=%d, rs=%d\n",
 		__FUNCTION__, __LINE__,
-		si->state, req->flags, res->flags, req->l, req->o, res->l, res->o);
+		si->state, req->flags, res->flags, req->i, req->o, res->i, res->o);
 
 	if (unlikely(si->state == SI_ST_DIS || si->state == SI_ST_CLO)) {
 		/* check that we have released everything then unregister */
@@ -3370,11 +3370,11 @@
 
 
 		chunk_printf(&msg,
-			     "  req=%p (f=0x%06x an=0x%x l=%d o=%d pipe=%d fwd=%d)\n"
+			     "  req=%p (f=0x%06x an=0x%x i=%d o=%d pipe=%d fwd=%d)\n"
 			     "      an_exp=%s",
 			     sess->req,
 			     sess->req->flags, sess->req->analysers,
-			     sess->req->l, sess->req->o,
+			     sess->req->i, sess->req->o,
 			     sess->req->pipe ? sess->req->pipe->data : 0,
 			     sess->req->to_forward,
 			     sess->req->analyse_exp ?
@@ -3400,11 +3400,11 @@
 			     sess->req->total);
 
 		chunk_printf(&msg,
-			     "  res=%p (f=0x%06x an=0x%x l=%d o=%d pipe=%d fwd=%d)\n"
+			     "  res=%p (f=0x%06x an=0x%x i=%d o=%d pipe=%d fwd=%d)\n"
 			     "      an_exp=%s",
 			     sess->rep,
 			     sess->rep->flags, sess->rep->analysers,
-			     sess->rep->l, sess->rep->o,
+			     sess->rep->i, sess->rep->o,
 			     sess->rep->pipe ? sess->rep->pipe->data : 0,
 			     sess->rep->to_forward,
 			     sess->rep->analyse_exp ?
@@ -3544,9 +3544,9 @@
 				     curr_sess->task->calls);
 
 			chunk_printf(&msg,
-				     " rq[f=%06xh,l=%d,an=%02xh,rx=%s",
+				     " rq[f=%06xh,i=%d,an=%02xh,rx=%s",
 				     curr_sess->req->flags,
-				     curr_sess->req->l,
+				     curr_sess->req->i,
 				     curr_sess->req->analysers,
 				     curr_sess->req->rex ?
 				     human_time(TICKS_TO_MS(curr_sess->req->rex - now_ms),
@@ -3565,9 +3565,9 @@
 						TICKS_TO_MS(1000)) : "");
 
 			chunk_printf(&msg,
-				     " rp[f=%06xh,l=%d,an=%02xh,rx=%s",
+				     " rp[f=%06xh,i=%d,an=%02xh,rx=%s",
 				     curr_sess->rep->flags,
-				     curr_sess->rep->l,
+				     curr_sess->rep->i,
 				     curr_sess->rep->analysers,
 				     curr_sess->rep->rex ?
 				     human_time(TICKS_TO_MS(curr_sess->rep->rex - now_ms),