In FileBackend/FileOp:

In FileBackend/FileOp:
* Replaced 'media' portion of container names with the repo name. This makes it easy for multiple repos to use the same backend without 'wikiId' hacks. Full container names are now like <wiki>-<repo>-<zone> (or <repo>-<zone> if 'wikiId' is set to an empty string).
* Restricted isValidContainerName() more in light of Azure portability and shorted shard suffix.
* Bumped $maxCacheSize to 75 storage paths.
* Code comment cleanups and additions.
Unit tests:
* Updated related tests and marked testBug29408() as broken (I can't find the problem).
* Reduced leakage in UploadFromUrlTestSuite a bit.