Implement asynchronous multi-master replication #270
async-master-master review fixes

* Remove a bogus message at the start of FindLibUUID.cmake.
* Move cluster_add_node to cluster.
* Extract UUID API into a (potentially) platform-independnent header
  tt_uuid.
* Add error codes for error messages used in UUID generation,
  triggers and consistency checks.
* Cleanup.
Add support for native uuid library on FreeBSD
Minor tweaks (wrapping up review changes for alter.cc).
Merge branch 'async-master-master-v2'