Define tracing unit tests with proper log level.
Fix bug in schema merging.

Also catches an exception that should not occur in the first place. Once we
migrate to Spirit X3, none of these will remain.
Implement flow control from indexers to ingestors.

Because the indexing process consumes most of the CPU time, it's easy to
overload this bottleneck by the much faster ingestors. Indexers now send back
to the ingestors their current delay until they finish processing. Ingestors
then defer sending segments for that reported timeout period.
Tune Bro log file parsing.