Set limit to 255 for Text type in MySQL Driver

MySQL Driver:
*set limit to 255 characters for Text type (VARCHAR)
*call "SET SESSION sql_mode='TRADITIONAL'" on opening database - needed to turn warnings about trimming string values into SQL errors
*practical solution for 'Kexi shows no indication that text is trimmed' bug in case of MySQL: error is displayed eg. "Record inserting on the server failed.Message from server: Data too long for column 'hn' at row 1. SQL statement: INSERT INTO table4 (hn) VALUES ('...................'). Server result: 1406"

More info on VARCHAR support in databases: http://www.ispirer.com/wiki/sqlways/mysql/data-types/varchar_n

CCBUG:301277
CCBUG:301136
REVIEW:105182
FIXED-IN:2.4.3