Instead of hoping that we can get a racy entry by going real fast and praying real hard, just create a racy entry.
Use legitimate (existing) object IDs in tests so that we have the ability to turn on strict object validation when running tests.
Windows defines `timeval` with `long`, which we cannot sanely cope with. Instead, use a custom timeval struct.
Ensure that `git_index_read_index` clears the uptodate bit on files that it modifies. Further, do not propagate the cache from an on-disk index into another on-disk index. Although this should not be done, as `git_index_read_index` is used to bring an in-memory index into another index (that may or may not be on-disk), ensure that we do not accidentally bring in these bits when misused.
Ensure that `git_index_read_tree` clears the uptodate bit on files that it modifies.
Test that entries are only smudged when we write the index: the entry smudging is to prevent us from updating an index in a way that it would be impossible to tell that an item was racy. Consider when we load an index: any entries that have the same (or newer) timestamp than the index itself are considered racy, and are subject to further scrutiny. If we *save* that index with the same entries that we loaded, then the index would now have a newer timestamp than the entries, and they would no longer be given that additional scrutiny, failing our racy detection! So test that we smudge those entries only on writing the new index, but that we can detect them (in diff) without having to write.
Keep track of entries that we believe are up-to-date, because we added the index entries since the index was loaded. This prevents us from unnecessarily examining files that we wrote during the cleanup of racy entries (when we smudge racily clean files that have a timestamp newer than or equal to the index's timestamp when we read it). Without keeping track of this, we would examine every file that we just checked out for raciness, since all their timestamps would be newer than the index's timestamp.