hg: shenandoah/jdk9/hotspot: Cancel events should print cause, and fire only once.

[ashipile at redhat.com]

Changeset: 678dca371148
Author:    shade
Date:      2016-11-25 15:35 +0100
URL:       http://hg.openjdk.java.net/shenandoah/jdk9/hotspot/rev/678dca371148

Cancel events should print cause, and fire only once.

! src/share/vm/gc/shenandoah/shenandoahHeap.cpp
! src/share/vm/gc/shenandoah/shenandoahHeap.hpp
! src/share/vm/gc/shenandoah/shenandoahHeap.inline.hpp