MEDIUM: stream: return the stream upon accept()

The function was called stream_accept_session(), let's rename it
stream_new() and make it return the newly allocated pointer. It's
more convenient for some callers who need it.
diff --git a/include/proto/stream.h b/include/proto/stream.h
index 02992fd..820cf47 100644
--- a/include/proto/stream.h
+++ b/include/proto/stream.h
@@ -36,7 +36,7 @@
 
 extern struct data_cb sess_conn_cb;
 
-int stream_accept_session(struct session *sess, struct task *t);
+struct stream *stream_new(struct session *sess, struct task *t);
 
 /* perform minimal intializations, report 0 in case of error, 1 if OK. */
 int init_stream();