Dummy predicate example.
Some small fixes (There are more).

I hope I'll have time in a couple of days to discuss fixes.
Concurrency: add initial versioning for search operation
Refactoring: extract method
Concurrency: initial versioning for insert
Concurrency: add right link to InnerEntry
Concurrency: search in right entries if there was split
Fix compilation
Large compilation fix
Hack: covariant cast
Fix compilation
Add test for basic inserting into Gist