Edit updater.refresh() and install of compressed metadata.

1. Raise an exception for clients that do not wish to automatically fetch a Root file when an expired version is loaded from disk.

2. Properly 'install' compressed metadata downloaded.  The compressed version of the rolename was added to the fileinfo store, which prevented detection of changed metadata and would unintentionally cause compressed metadata to always refresh (only the fileinfo of uncompressed metadata is stored and compared.)

3. Rename unsafely_verify_compressed_metadata_file() variable names, so that they match the other verify functions.