Beefed up transaction implementation, still needs tests
and cleanup of nested transaction queues.
Left todo:
- Fix commented out tests
- Fix oracle driver's transactions
* 'master' of github.com:tgriesser/knex:
oracle - fixed first and added more tests
Fix bad argument to builder.whereNull
don't throw away the postgres client's password
oracle - fixed SQL for dropping multiple columns
Do not attempt to release undefined connections from pool, #414