Bug about Major compaction and Minor Compaction in copy cat

[Terry Tan]

Hi Jordan,

currently ,the major compaction and minor compaction are running respectively, which means ,by coincidently, maybe they will run at the same time, there is a step by which we can change the 
the segments list ,like segmentlist.put(); if the minor compaction do this step after the major compaction,
maybe the major compacted segment will be discarded.