BUG/MEDIUM: http: 100-continue responses must process the next part immediately

Since commit d7ad9f5 ("MAJOR: channel: add a new flag CF_WAKE_WRITE to
notify the task of writes"), we got another bug with 100-continue responses.
If the final response comes in the same packet as the 100, then the rest of
the buffer is not processed since there is no wake-up event.

In fact the change above uncoverred the real culprit which is more
likely session.c which should detect that an earlier analyser was set
and should loop back to it.

A cleaner fix would be better, but setting the flag works fine.
This issue was introduced in 1.5-dev22, no backport is needed.

src/proto_http.c

@@ -5932,6 +5932,7 @@ int http_process_res_common(struct session *t, struct channel *rep, int an_bit,
 			txn->status = 0;
 			t->logs.t_data = -1; /* was not a response yet */
 			rep->analysers |= AN_RES_WAIT_HTTP | an_bit;
+			rep->flags |= CF_WAKE_WRITE;
 			return 1;
 		}
 		else if (unlikely(txn->status < 200))