Merge lp://staging/~jderose/filestore/no-more-ext into lp://staging/filestore

I've generally chosen pragmatism over purity in the design of dmedia. A good example of this is using a base32-encoded content-hash (_id) so that the canonical filename can be constructed in the simplest way possible.

Another example was including a file extension on the canonical file name. The rationale was:

 1) Some software doesn't work without the file extension, which is used for type determination

 2) Including the file extension would allow a vanilla web server like Apache to server the files with the correct Content-Type

However, I've changed my mind on the file extension, for a few reasons, the biggest reason being that with the file extension we don't have a true canonical filename anymore, which makes it difficult to make these critical code paths as robust as they need to be. Using the untrusted file extension to construct a filename is also a potential security vulnerability (although carefully validated the extension).

I may add similar functionality back eventually, but not on the canonical filenames. If a content-hash based name is needed within the filestore with an extension, I feel the correct route is to symlink to the canonical file. So for example the canonical filename would be:

  files/V3/ODQNYR62VFR4KGIKS3IE4SQKCYI7GIYLPD3UA4RDSCR7HG

And the symlink name would be:

  symlinks/V3/ODQNYR62VFR4KGIKS3IE4SQKCYI7GIYLPD3UA4RDSCR7HG.txt

The canonical filename is critical for data durability, is not the place for software compatibility hacks.