Transaction Control

[twalmsley]

Change the DB transactions to default to WRITE for the *InTransaction() methods and provide overloaded versions with a transaction control parameter of type TxnType.

This is because the default for local TDB instances is READ_PROMOTE which might fail if, at the time of promotion, there have been some intervening updates.

Transactions on the RDFConnection for remote databases don't support READ_PROMOTE, so they are already WRITE transactions by default.

[twalmsley]

I'm going to change this so that the callers have to select the READ or WRITE version explicitly, and the same for runInTransaction - it will become runInWriteTransaction and runInReadTransaction.