caching location to be non-local

[martindurant]

Proposal to have the target location for file caching to be something other than the local filesystem, e.g., a scratch bucket for initial copy of a dataset from one cloud platform to another.

In parallel, the same_names=True parameter should be changed to allow a certain number of parent filenames to be stored as part of the cached file name.

[scottyhq]

this would be neat, just wanted to point out a use-case where this has come up #476 (comment)