I can recreate the file, set the modification time, but can't forge creation
time, thus cannot recreate the exact same uploaded file twice.
This change targets this problem.
As this is a very rarely used flag, this is enabled only if the CAMLI_DEBUG
environment variable is true - such as the other "gross" options
(statcache, sqlitecache...).
Change-Id: I99c7805898ed97883043de4e7dcec23a472e462c