When following error message is shown, then it will get converted to the
correct Exception classs of NotNullConstraintViolationException:

  PDOException: SQLSTATE[HY000]: General error: 1364 Field '...' doesn't have a
  default value

it is best practice to implement retry logic for transactions that are aborted because of deadlocks or timeouts. this makes such method available inside the DBAL and also add detection for errors where retrying makes sense in the different database drivers

- 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

Hopefully final fixes. Added phpdoc @inheritdoc where it were missing. Added MysqlConnection::getWrappedResourceHandle(). MysqliStatement::fetchAll() now decide fetch style if none is set, instead of letting fetch() do it on every call.