import downloader complete (untested)

Made some api changes.

listImportableContents needs to provide the size
of the data, so the downloader can check disk free space.

retrieveExportWithContentIdentifier is passed the filepath to write to

Use temporary "CID" key during download of a ContentIdentifier from a
remote, so withTmp can be used and then move the content to the real key
once it's known.

Types/Remote.hs

@@ -43,6 +43,7 @@ import Utility.Metered
 import Git.Types (RemoteName)
 import Utility.SafeCommand
 import Utility.Url
+import Utility.DataUnits
 
 type RemoteConfigKey = String
 
@@ -243,11 +244,11 @@ data ExportActions a = ExportActions
 
 data ImportActions a = ImportActions
 	-- Finds the current set of files that are stored in the remote,
-	-- along with their content identifiers.
+	-- along with their content identifiers and size.
 	--
 	-- May also find old versions of files that are still stored in the
 	-- remote.
-	{ listImportableContents :: a (Maybe (ImportableContents ContentIdentifier))
+	{ listImportableContents :: a (Maybe (ImportableContents (ContentIdentifier, ByteSize)))
 	-- Retrieves a file from the remote. Ensures that the file
 	-- it retrieves has the requested ContentIdentifier.
 	--
@@ -257,9 +258,10 @@ data ImportActions a = ImportActions
 	, retrieveExportWithContentIdentifier 
 		:: ExportLocation
 		-> ContentIdentifier
-		-> (FilePath -> a Key)
-		-- ^ callback that generates a key from the downloaded content,
-		-- it may rename or delete the file
+		-> FilePath
+		-- ^ file to write content to
+		-> a (Maybe Key)
+		-- ^ callback that generates a key from the downloaded content
 		-> MeterUpdate
 		-> a (Maybe Key)
 	-- Exports content to an ExportLocation, and returns the