merge of r7926 ENG-192 Fix for writer queue length statistic

git-svn-id: http://svn.terracotta.org/svn/ehcache@8016 b9324663-ca0f-0410-8574-be9b3887307d
merge of r7926 ENG-192 Fix for writer queue length statistic

git-svn-id: http://svn.terracotta.org/svn/ehcache@8017 b9324663-ca0f-0410-8574-be9b3887307d