Move establishing user auth into a fixture.

So it can be reused.
implement experimental closet handling

This uploads a binary file to "other" storage and creates
a canonical uri tiddler.

The current implementation is just to stub out the ideas. A
real solution would use something like S3 for real storage.
Switch to using to using s3/boto for storage of binaries.

Same principle, data just goes to a public-read bucket on s3.

So that's cool. Next step is to change the binary uploaders
to post to /closet/<tank> instead of PUT to tiddler bags.
Merge branch 'master' into closet
remove unused class member
Adjust binary handling some more

* if a non-binary is posted, then save as a normal tiddler
* if a binary is PUT, then use a validator to save the content on
  s3
* change POST to by default return 204, not 303, which makes use
  from xhr tidier

Not sure about error handling...

Next: adjust client side code
Ensure validators are only added once.
Switch over the file uploader to use a POST to /closet

This ensures that we'll save some memory and processing
when uploading binaries.