We want a header not a footer after all. (Breaks one test)

This is necessary for making a Bucket that can convert to an ERAT.
Pass in a flag for whether the file is new or not.

The header being all 0's is not an acceptable way to determine this. Not all RAFs start off with all 0's, and it can cause odd behaviour in tests too.
Fix error message
Update test harness
Update from purge-db4o
Update from db4o (need RandomAccessBucket aspect)
Need RAF*
Add new class EncryptedRandomAccessBucket. This uses the same crypto as ERAT, and writes a header, so it can be converted to an ERAT.