Version 4.7 published

This version improves transaction handling by allowing an explicit ROLLBACK to terminate an SQL routine such as a store procedure. (COMMIT is not allowed inside a routine since it would cause premature termination of the routine.) New error messages for this behaviour means that the client libraries OSPLink and PyrrhoLink have been updated. Transaction behaviour is more transparent in the command prompt tool PyrrhoCmd, for example by the use of a special prompt SQL-T> inside transactions. Other fixes help with tables constraints, parsing of error handlers and default values for strings.