Stop --track-renames deleting case folded source files - fixes #1094

What was happening is that when Move was implemented as Copy + Delete,
MoveFile was seeing the files didn't need transferring (because they
were identical) then deleted the source.

The fix uses Move instead and patches onedrive to disallow a case
folded identical copy (which errors with 500 error)

fs/sync.go

@@ -593,17 +593,23 @@ func (s *syncCopyMove) tryRename(src Object) bool {
 	Stats.Checking(src.Remote())
 	defer Stats.DoneChecking(src.Remote())
 
+	// Calculate the hash of the src object
 	hash := s.renameHash(src)
 	if hash == "" {
 		return false
 	}
 
+	// Get a match on fdst
 	dst := s.popRenameMap(hash)
 	if dst == nil {
 		return false
 	}
 
-	err := MoveFile(s.fdst, s.fdst, src.Remote(), dst.Remote())
+	// Find dst object we are about to overwrite if it exists
+	dstOverwritten, _ := s.fdst.NewObject(src.Remote())
+
+	// Rename dst to have name src.Remote()
+	err := Move(s.fdst, dstOverwritten, src.Remote(), dst)
 	if err != nil {
 		Debugf(src, "Failed to rename to %q: %v", dst.Remote(), err)
 		return false

onedrive/onedrive.go

@@ -600,6 +600,10 @@ func (f *Fs) Copy(src fs.Object, remote string) (fs.Object, error) {
 		return nil, err
 	}
 
+	if strings.ToLower(srcObj.remote) == strings.ToLower(remote) {
+		return nil, errors.Errorf("can't copy %q -> %q as are same name when lowercase", srcObj.remote, remote)
+	}
+
 	// Create temporary object
 	dstObj, leaf, directoryID, err := f.createObject(remote, srcObj.modTime, srcObj.size)
 	if err != nil {