AbstractCache.cacheToDisk() spams log

[jcogilvie]

There's an incessant log message about using the default 8k buffer because none was specified in AbstractCache.cacheToDisk when creating the BufferedOutputStream.

This is a trivial fix; we just changed the line to add:

BufferedOutputStream ostream = new BufferedOutputStream(new FileOutputStream(file), BUFFER_SIZE);

where BUFFER_SIZE is 8192. It cleans the logs a bit.