Switch to using EasSyncBase for mail downsync.

Also terminate any sync upon encountering its first error --
if we see an io, auth, etc. error, there's no point in trying
further folders.

Change-Id: I08b9a3078b3f17774a6f76a49ff87d37686e694e
(cherry picked from commit 9a2230380dc95e4b6dd66b14a43d8007dc5f784e)
4 files changed