rendermanager.py 2.8: many improvements.

- fixed handling of dependencies when rendering multiple shots concurrently.
- the render manager can now be terminated (by pressing CTRL-C) during updates of the dependency databases.
- only print pings for machines rendering the current shot.
- fixed crash when the log file for a given machine does not exist.
implemented ray types.
rendermanager.py 2.9: fixed crash when multiple log files were missing.