[mbaszlyr] Automatically growing filesystem

Place a filesystem in a file-based container, and have the file container automatically grow and shrink as files are added and deleted.

The motivation, though I don't know if it will work, is a better implementation of encrypted /tmp which is destroyed on shutdown (a new random key is generated on boot), but not wanting to limit to a predefined container size (e.g., a separate encrypted partition for /tmp).  We also wish to avoid the encfs or ecryptfs weaknesses of being able to see the approximate file sizes, number of files, or directory structure.  The metadata in the file based container should be sufficiently encrypted so as not to be able to see that information.