Add failing test discovered in opam-mirror

[reynir]

This failing test uses a 64 MB filesystem. It first writes two files of size 2 MiB. Then it disconnects and connects again, and sets one of the files to a value slightly larger than 2 MiB. Then chamelon fails and complains about lack of space.

I can try to minimize the test case as the large-ish sizes result in a lot of debug output.

[reynir]

I tried the same test without reconnecting and then it succeeds.

[reynir]

I tried using smaller files (2KB instead of 2MB), but then I could not reproduce. Rewriting with a small file (2 KB) works fine though. I also disabled debug logging when writing the large files to reduce the log output from ~30K lines to ~1600 lines.

[yomimono]

Thanks very much for this test case. I'm about to page this project back into my brain and will see what I can figure out.