[IIAB] gutenberg cached files

[Joel Steres]

Greetings,

The Gutenberg project references a lot of "generated" files which are
not in the ibiblio mirror we use.  The mirror just contains a broken
symlink at cache/generated.  Much of it appears to be various ebook
formats.  I will continue based on the assumption that cached content
is unavailable and so I will filter it out.  If we should try to
obtain/include the cached content let me know.

Joel