Improvements to the TreeIntegrity utility program. Switching
from the ConcurrentTree to the ReadTree when opening the
tree in read-only mode. The ConcurrentTree cannot open a tree
in read-only mode that does not have the -infinity key which is
inserted at the beginning of the tree if the key is absent.
Merge branch 'master' into skiplist-newdelete

Conflicts:
	hydra-data/src/test/java/com/addthis/hydra/data/tree/TreeIntegrity.java