Fix resuming of downloads, which do not have a transfer info file to read.
When checking upload progress, use the MVar, rather than re-reading
the info file.
Catch exceptions in the transfer action. Required a tryAnnex.
I had to, I hope temporarily, lose my nice Annex newtype, and use a type
synonym. This because I cannot find a way to derive a MonadBaseControl
instance of the Annex newtype. I've emailed Bas van Dijk in hope he can
help get the newtype back.
Otherwise appears to build & work.
