Fix for Issue #7, generalizing multi-line schemas tests:

- Made Repository implement Closeable and changed all Repository implementations accordingly.
- Moved the LocalFileSystem's tests to a new AbstractTestPersistentRepository class, which LocalFS and ZK tests extend.
- Actually found a bug in the previous implementation of the multi-line test and LocalFS repo, and fixed those bugs.
- Enabled (and added config for) the Jetty capability to hook into the shutdown event, to make sure repos are always closed.