Case change in file name does not cause backfill to use new file

[crazyfraggle]

Repro step:

1. Build a project to populate the cache
2. Rename a file to a different capitalization, but still the same name.
3. Re-build project. File is still fetched from cache, and will have same capitalization as original.

Issue seen on MacOS.

[dobesv]

Was the filename case changed in git as well? I wonder if this is related to the way backfill uses git to get the hashes, maybe git is reporting the old filename because it still has that filename in its list of files.