Updated CHANGELOG
Started work on multi-session
Fixed index statistics
[new index structure] BTreeIndex constructor takes data type into account.
[new index structure] Capability of writing empty indices.
[new index structure] Create BTree in IndexFactory.
[new index structure] Bugfix in IndexFactory.
[new index structure] PageUsageStats uses HardDrive storage.
[new index structure] merge master
[new index structure] Additional BTreeStorageManager test.
Merge branch 'new-index-structure' into prefix-sharing

Conflicts:
	src/org/zoodb/internal/server/index/BTreeIndex.java
	src/org/zoodb/internal/server/index/BTreeIndexNonUnique.java
	src/org/zoodb/internal/server/index/BTreeIndexUnique.java
	src/org/zoodb/internal/server/index/IndexFactory.java
	src/org/zoodb/internal/server/index/btree/BTree.java
	tst/org/zoodb/test/index2/performance/PageUsageStats.java
[prefix sharing] Manual merge between new-index-structure and prefix-sharing branches.