[migration] set a cnxset before process_script() Not pretty, but I don't have a better idea right now and this at least ensures migration scripts get run in the expected environment and can access sql stuff as before.

option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')