[server] fix db-dump with sqlite
'gzip -c dbname > backupfile' needs to go through the shell.
change_attribute_type('CWCache', 'timestamp', 'TZDatetime')
change_attribute_type('CWUser', 'last_login_time', 'TZDatetime')
change_attribute_type('CWSource', 'latest_retrieval', 'TZDatetime')
drop_attribute('CWSource', 'synchronizing')
add_attribute('CWSource', 'in_synchronization')