Multi-table update and delete queries are not supported

[gbadner]

Currently, updates and deletes that affect multiple entity tables are not supported

For example, suppose Folder, Document, and SymbolicLink all extend abstract File, which has a name property, and uses InheritanceType.TABLE_PER_CLASS.

That means that Folder, Document, and SymbolicLink each has it's own DB table, each having a name column.

In order to delete all File entities with name like 'Enron%', rows have to be deleted from all 3 tables.

Fixing this would require something like MultiTableUpdateExecutor and MultiTableDeleteExecutor.

[gavinking]

I have an initial, fairly crappy, fix for this in #325.