manifest: use property instead of field for manifest revlog storage The file caches we're using to avoid reloading the manifest from disk everytime has an annoying bug that causes the in memory structure to not be reloaded if the mtime and the size haven't changed. This causes a breakage in the tests because the manifestlog is not being reloaded after a commit+strip operation in mq (the mtime is the same because it all happens in the same second, and the resulting size is the same because we add 1 and remove 1). The only reason this doesn't affect the manifest itself is because we touch it so often that we had already reloaded it after the commit, but before the strip. Once the entire manifest has migrated to manifestlog, we can get rid of these properties, since then the manifestlog will be touched after the commit, but before the strip, as well.