doctrine:migrations:diff is generating SQL for MEDIUMTEXT fields

[jamestooks]

The diff command is generating SQL everytime even if the database is already up to date.

For example:

• I run diff to generate SQL to update a field to now be a MEDIUMTEXT field
• I execute the migration
• I run diff again and the same SQL is generated again

[stof]

This should be reported against the DBAL project, which is responsible for comparing schemas and generating the list of SQL queries needed to go from one to the other.