Fix fast file cache reduction

[orbikm]

• Previously, an attempt was made to speed up the most naive case of EzLink conversion, where there is a unique filename across the entire site. This would allow a simple dictionary lookup instead of a full Prefix Trie search (which is more expensive).

  Previously, it incorrectly trimmed all files from the file cache when reducing it to unique items, because the dictionary comprehension had an inverted comparison operator.

  Now, unique file names will be directly converted via the fast file cache.

[orbikm]

This will be going into the 0.12.0 release.