fix the potential bug....
merge conflicts....

Conflicts:
	src/main/java/com/ctriposs/tsdb/level/MemTableStoreLevel.java
	src/main/java/com/ctriposs/tsdb/storage/CodeBlock.java
	src/main/java/com/ctriposs/tsdb/storage/DBWriter.java
	src/main/java/com/ctriposs/tsdb/storage/TimeBlock.java