hg: shenandoah/jdk10: Do not put down update-refs-in-progress flag concurrently

[ashipile at redhat.com]

Changeset: dc779781dd5e
Author:    shade
Date:      2018-01-22 12:04 +0100
URL:       http://hg.openjdk.java.net/shenandoah/jdk10/rev/dc779781dd5e

Do not put down update-refs-in-progress flag concurrently

! src/hotspot/share/gc/shenandoah/shenandoahConcurrentThread.cpp
! src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp
! src/hotspot/share/gc/shenandoah/shenandoahHeap.hpp
! src/hotspot/share/gc/shenandoah/shenandoahMarkCompact.cpp