Releases for Version Control API -- Git backend

Changes:

- don't use our file cache anymore.
- #484372: Improve the cache Improve the cache
- removes the evil cache functions (They are not used anymore)
- review cache_get return before use it
- clear cache on uninstall

Fixes:

- actually pass the missing parameter merge on _versioncontrol_git_parse_items()
- avoid empty tagname (do not use the ":short" suffix on refname inside git-for-each-ref format)
- fix: update vc api interaction on repo add/edit (replace hook_versioncontrol_extract_repository_data with hook_versioncontrol_repository_submit(). )
- remove hook documentation (make the code less redundant)