Fixed undefined index notice when attempting to reconnect a MasterSlaveConnection after close has called

[DBAL-717] Fix bug in MasterSlaveConnection with keepSlave option and switch back after transaction.

- Fixed docblocks
- Removed return statements on void methods
- Cleaned up unused private / local variables
- Fixed license issues
- Removed SVN leftovers
- Fixed doctrine-project.org links
- Added line breaks before return statements

[DBAL-335] Fix nasty bug in MasterSlaveConnection, connecting and writing to slave when using keepSlave option.

Add option to keep the slave in master/slave setups. You can call $conn->connectTo("slave") to get back to the slave connection