Merge branch 'mm/verify-filename-fix' into maint

"git diff COPYING HEAD:COPYING" gave a nonsense error message that
claimed that the treeish HEAD did not have COPYING in it.

* mm/verify-filename-fix:
  verify_filename(): ask the caller to chose the kind of diagnosis
  sha1_name: do not trigger detailed diagnosis for file arguments

builtin/grep.c

@@ -928,7 +928,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	if (!seen_dashdash) {
 		int j;
 		for (j = i; j < argc; j++)
-			verify_filename(prefix, argv[j]);
+			verify_filename(prefix, argv[j], j == i);
 	}
 
 	paths = get_pathspec(prefix, argv + i);