MySQL - TEXT and BLOB columns can't have a default value

This is a follow up to MDL-6206 (adding a quiz fails on some MySQL 5 setups because it relies on using a default value for a TEXT column)

According to the MySQL documentation TEXT and BLOB aren't allowed to use default values - http://dev.mysql.com/doc/refman/5.0/en/blob.html - but a quick search of the .sql files in moodle using a regexp like

/ text[^rn,]+default/i

finds several places where text columns are setup with a default value - obviously it would require much more in depth checking to find out if any of these default values are required anytime a row is created.

As noted in the previous bug MySQL only seems to enforce it's no default values for TEXT or BLOB rule with certain values of the sql_mode server variable (I think the default value of sql_mode in MySQL 5.0.22 includes the STRICT_TRANS_TABLES option which causes any query trying to use a default value to fail)