sync: Fix double merge conflict resolution handling.

Ie, when there'a a conflicted merge we may get foo.variant-xxxx
created in a merge. If a second merge conflict occurs on that new file,
it was not falling back to putting in the whole key (which should stop
the merge conflicts happening for good, but is ugly).

Command/Sync.hs

@@ -302,7 +302,7 @@ mergeFile file key
 	| otherwise = go $ shortHash $ key2file key
   where
 	varmarker = ".variant-"
-	doubleconflict = varmarker `isSuffixOf` (dropExtension file)
+	doubleconflict = varmarker `isInfixOf` file
 	go v = takeDirectory file
 		</> dropExtension (takeFileName file)
 		++ varmarker ++ v