Thanks Markus Holtermann, Collin Anderson and Tim Graham for the reviews.

Pass type to sql_alter_column*.

This helps databases which need the database type when changing the default
(Just like MySQL needs it for changing null…)

The _size attribute is used in File.size but FieldFile overrides it.

Browser names should be passed as a comma separated list to the --selenium flag.

Thanks Tim Graham, Simon Charette and Moritz Sichert for review and discussion.