Use non-pooled SegmentedFile builders when bulk loading
Patch by Sam Tunnicliffe, reviewed by brandonwilliams for CASSANDRA-6272
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	src/java/org/apache/cassandra/io/sstable/SSTableReader.java
	test/unit/org/apache/cassandra/io/sstable/SSTableReaderTest.java