[cache] url with : cannot be cached

URL with a `:` in the pathnam (jcr:content sic!) cannot be cached. I assume directory cannot be created.

Start by reproducing the cache failure with a URL whose pathname contains a colon, such as `jcr:content`, and trace the cache handling for that pathname. No file or test is named in the issue; done means that the URL can be cached successfully and the relevant regression is covered by a test.

Written by the indexing model from the issue text.