version the cache by the KEY_PREFIX instead of VERSION, as VERSION is an int
Merge branch 'release-0.10' of github.com:learningequality/ka-lite into cache_by_version
moving import to top of file, adding comment to version.py
Merge branch 'release-0.10' of github.com:learningequality/ka-lite into cache_by_version
Merge pull request #553 from bcipolli/cache_by_version

Do not reuse cache entries after version change
Thanks for the comments, @jamalex !  Per my comments, merging as-is!