Fixing a bug in Overlap computation.
Better keyrange management for resharding.

Now the split snapshot manifest contains the keyrange of the
server that took the snapshot, as well as the part that was
snapshot.

blp_recovery now contains the keyrange of the source shard.
That way we can find a server for it.
The player side just computes the overlap before asking the
server.
Using real KeyRange structure in binlog toolchain.
Removing an unused limitation in keyspace coverage