Support filenames that start with a dash; when such a file is passed to a utility it will be escaped to avoid it being interpreted as an option.

Backend/SHA1.hs

@@ -20,6 +20,7 @@ import qualified Annex
 import Locations
 import Content
 import Types
+import Utility
 
 backend :: Backend Annex
 backend = Backend.File.backend {
@@ -31,7 +32,7 @@ backend = Backend.File.backend {
 sha1 :: FilePath -> Annex String
 sha1 file = do
 	showNote "checksum..."
-	liftIO $ pOpen ReadFromPipe "sha1sum" [file] $ \h -> do
+	liftIO $ pOpen ReadFromPipe "sha1sum" [utilityEscape file] $ \h -> do
 		line <- hGetLine h
 		let bits = split " " line
 		if null bits

Backend/URL.hs

@@ -51,6 +51,6 @@ downloadUrl :: Key -> FilePath -> Annex Bool
 downloadUrl key file = do
 	showNote "downloading"
 	showProgress -- make way for curl progress bar
-	liftIO $ boolSystem "curl" ["-#", "-o", file, url]
+	liftIO $ boolSystem "curl" ["-#", "-o", utilityEscape file, url]
 	where
 		url = join ":" $ drop 1 $ split ":" $ show key