PoolSvc: thread-checker cleanup and extra locking
PoolSvc::createCollection was marked as not thread-safe due to the use
of the pool::CollectionFactory singleton. Use the general PoolSvc
mutex to protect access to it and mark it as safe.
Also lock when calling registerPFN on the catalog as it is not clear
to me if the context-specific persistency lock is good enough.
Finally remove some unnecessary mutable, thread-checker annotations and update link dependencies.