partially complete gcrypt remote (local send done; rest not)

This is a git-remote-gcrypt encrypted special remote. Only sending files
in to the remote works, and only for local repositories.

Most of the work so far has involved making initremote work. A particular
problem is that remote setup in this case needs to generate its own uuid,
derivied from the gcrypt-id. That required some larger changes in the code
to support.

For ssh remotes, this will probably just reuse Remote.Rsync's code, so
should be easy enough. And for downloading from a web remote, I will need
to factor out the part of Remote.Git that does that.

One particular thing that will need work is supporting hot-swapping a local
gcrypt remote. I think it needs to store the gcrypt-id in the git config of the
local remote, so that it can check it every time, and compare with the
cached annex-uuid for the remote. If there is a mismatch, it can change
both the cached annex-uuid and the gcrypt-id. That should work, and I laid
some groundwork for it by already reading the remote's config when it's
local. (Also needed for other reasons.)

This commit was sponsored by Daniel Callahan.

Remote/Bup.hs

@@ -29,6 +29,7 @@ import Data.ByteString.Lazy.UTF8 (fromString)
 import Data.Digest.Pure.SHA
 import Utility.UserInfo
 import Annex.Content
+import Annex.UUID
 import Utility.Metered
 
 type BupRepo = String
@@ -78,8 +79,10 @@ gen r u c gc = do
   where
 	buprepo = fromMaybe (error "missing buprepo") $ remoteAnnexBupRepo gc
 
-bupSetup :: UUID -> RemoteConfig -> Annex RemoteConfig
-bupSetup u c = do
+bupSetup :: Maybe UUID -> RemoteConfig -> Annex (RemoteConfig, UUID)
+bupSetup mu c = do
+	u <- maybe (liftIO genUUID) return mu
+
 	-- verify configuration is sane
 	let buprepo = fromMaybe (error "Specify buprepo=") $
 		M.lookup "buprepo" c
@@ -96,7 +99,7 @@ bupSetup u c = do
 	-- persistant state, so it can vary between hosts.
 	gitConfigSpecialRemote u c' "buprepo" buprepo
 
-	return c'
+	return (c', u)
 
 bupParams :: String -> BupRepo -> [CommandParam] -> [CommandParam]
 bupParams command buprepo params =