Problem: `vim.pack.get()` always uses lockfile as the source for the
`rev` field. This is fast, but may be misleading in case of
a corrupted lockfile.
Solution: Compute revision from Git repo on disk if `info=true`
(default), use lockfile otherwise. This does increase execution time
(as a result of one extra `git ...` call for every plugin), but
`info=true` is already designed to be informative and not necessarily
fast.
8d100483e0
