Postgres folds all unquoted column names to lowercase, and doing this
allows that to work nicely without screwing up the queries for the other
database engines.
This removes the following error, caused by the MySQL Dialect using a
'varchar' for all columns over 256 characters in length, instead of
'text' for the largest:
2017/11/17 22:41:33 common_test.go:208: Error 1074: Column length too big for column 'Lua' (max = 21844); use BLOB or TEXT instead
