Preserve execute bits of unlocked files in v6 mode.

When annex.thin is set, adding an object will add the execute bits to the
work tree file, and this does mean that the annex object file ends up
executable.

This doesn't add any complexity that wasn't already present, because git
annex add of an executable file has always ingested it so that the annex
object ends up executable.

But, since an annex object file can be executable or not, when populating
an unlocked file from one, the executable bit is always added or removed
to match the mode of the pointer file.

Command/Unlock.hs

@@ -15,6 +15,7 @@ import Annex.Version
 import Annex.Link
 import Annex.ReplaceFile
 import Utility.CopyFile
+import Utility.FileMode
 
 cmd :: Command
 cmd = mkcmd "unlock" "unlock files for modification"
@@ -50,16 +51,17 @@ start file key = ifM (isJust <$> isAnnexLink file)
 
 performNew :: FilePath -> Key -> CommandPerform
 performNew dest key = do
+	destmode <- liftIO $ catchMaybeIO $ fileMode <$> getFileStatus dest
 	replaceFile dest $ \tmp -> do
-		r <- linkFromAnnex key tmp
+		r <- linkFromAnnex key tmp destmode
 		case r of
 			LinkAnnexOk -> return ()
 			_ -> error "unlock failed"
-	next $ cleanupNew dest key
+	next $ cleanupNew dest key destmode
 
-cleanupNew ::  FilePath -> Key -> CommandCleanup
-cleanupNew dest key = do
-	stagePointerFile dest =<< hashPointerFile key
+cleanupNew ::  FilePath -> Key -> Maybe FileMode -> CommandCleanup
+cleanupNew dest key destmode = do
+	stagePointerFile dest destmode =<< hashPointerFile key
 	return True
 
 startOld :: FilePath -> Key -> CommandStart