Use camel_folder_sync_message() to sync messages.

Use camel_folder_sync_message() to sync messages.

The imapx back end will handle sync_message requests at a much lower
priority than normal get_message requests, as is right and proper.

It would help if the front end would call the correct method, so that
the prioritisation actually works as expected. Otherwise, sync_message
requests end up having higher priority than the requests which are updating
flags and headers for changed folders -- leading to a crappy user experience.