Table name prefix for table migration_version

The doctrine migration class sets a default table name for storing its version information, which bypasses any formatting rules, e.g. a table name prefix. Calling the function setTableName() does apply the format defined, but one cannot call _createMigrationTable() afterwards. This results in a situation, where on one hand I can have the table automatically created with the "wrong" name and on the other hand have the class use the correct table name but not create it at first.

The attached patch is a simple solution to this dilemma, it added a call from the contructor to set the table name by the function call.