[prefix-sharing] Re-wrote root overfow code to avoid creating Pair objects.
[prefix-sharing] Re-wrote deletion to avoid creating of unnecessary objects.
Merge remote-tracking branch 'origin/prefix-sharing' into prefix-sharing

Conflicts:
	src/org/zoodb/internal/server/index/btree/BTree.java
[prefix-sharing] Re-wrote iterators to avoid iterating over a node's children to find the left/right siblings.
[prefix-sharing] Added extra information about children.
[prefix-sharing] Fixed several errors.