TODO:

Medium-prio:
* Provide ~100% automated test coverage of all functionality.
* Throw MWException "please create the bucket manually"
	if S3 bucket doesn't exist and createBucket() fails.

Low-prio:
* Implement doGetFileSha1Base36() in AmazonS3FileBackend.

Tests needed:
* simulate a private wiki in HooksTest (check URL of public/thumb zone).
* simulate a private wiki in BackendTest (check public/thumb bucket security).
* maybe add a high-level (non-decoupled) test?
	- upload a file via API. (and double-check)
	- check that thumbnails have been generated.
	- rename this file via API. (and double-check)
	- delete the file. (and double-check)
	- check that thumbnails were deleted.