Merge branch 'bc/racy-4gb-files'

The index file has room only for lower 32-bit of the file size in
the cached stat information, which means cached stat information
will have 0 in its sd_size member for a file whose size is multiple
of 4GiB.  This is mistaken for a racily clean path.  Avoid it by
storing a bogus sd_size value instead for such files.

* bc/racy-4gb-files:
  Prevent git from rehashing 4GiB files
  t: add a test helper to truncate files

t/helper/test-tool.h

@@ -79,6 +79,7 @@ int cmd__submodule_config(int argc, const char **argv);
 int cmd__submodule_nested_repo_config(int argc, const char **argv);
 int cmd__subprocess(int argc, const char **argv);
 int cmd__trace2(int argc, const char **argv);
+int cmd__truncate(int argc, const char **argv);
 int cmd__userdiff(int argc, const char **argv);
 int cmd__urlmatch_normalization(int argc, const char **argv);
 int cmd__xml_encode(int argc, const char **argv);