I am an abstract class that collects some of the operations common to all mail database files.

	file operations
	delete openOn: rename: save

	read-write
	readFrom: writeOn:

	error reporting	top
	reportInconsistency Report that the index file is not consistent with the messages file.

	file operations	top
	delete Delete this file.
	openOn: Initialize myself from the file with the given name.
	rename: Rename this file.
	save Atomically save a representation of this object to its file. The old file is renamed to '<oldname>.bak' before the new file is written. If the write operation fails, the old file may be restored by renaming it. If it succeeds, the .bak file is deleted.

	read-write	top
	readFrom: Subclasses must override this method to provide a means of reading themselves into memory.
	writeOn: Subclasses must override this method to provide a means of writing themseves out on their files.

	instance creation	top
	openOn: Answer a new instance of me, backed by the file with the given name.