new block layout (suffixes - first 4K, RB next N blocks) for faster lookup/write and less disk space

Conflicts:
	src/java/org/apache/cassandra/db/index/search/OnDiskSA.java
	src/java/org/apache/cassandra/db/index/search/OnDiskSABuilder.java
release resources sooner in SASI
SASI - only open/close SA files when performing a search (do not keep them open)
SSTW/SSTR - allow non-SA secondary indices :)
fix search to consider all of the suffixes via iteration (+ test)