Make sure unfinished compaction files are removed.

Patch by marcuse; reviewed by yukim for CASSANDRA-8124
Refactor how we track live size

Patch by marcuse; reviewed by yukim for CASSANDRA-7852
Merge branch 'cassandra-2.1' into trunk

Conflicts:
	src/java/org/apache/cassandra/db/compaction/CompactionManager.java
	src/java/org/apache/cassandra/db/compaction/Upgrader.java
	src/java/org/apache/cassandra/io/sstable/SSTableRewriter.java
	test/unit/org/apache/cassandra/db/compaction/AntiCompactionTest.java