This is a hack to make hydra-queue-runner free its temproots
periodically, thereby ensuring that garbage collection of the
corresponding paths is not blocked until the queue runner is
restarted.
It would be better if temproots could be released earlier than at
process exit. I started working on a RAII object returned by functions
like addToStore() that releases temproots. However, this would be a
pretty massive change so I gave up on it for now.
* Unify SSH code in SSHStore and LegacySSHStore.
* Fix a race starting the SSH master. We now wait synchronously for
the SSH master to finish starting. This prevents the SSH clients
from starting their own connections.
* Don't use a master if max-connections == 1.
* Add a "max-connections" store parameter.
* Add a "compress" store parameter.
This allows a RemoteStore object to be used safely from multiple
threads concurrently. It will make multiple daemon connections if
necessary.
Note: pool.hh and sync.hh have been copied from the Hydra source tree.
