Prune large blobs

Problem to solve

Partial clone helps me avoid downloading large files I don't need, but over time as I checkout different commits, I will still accumulate more and more objects that I don't need or want.

Further details

Maybe there is a Git alias that could be written to list out the large blobs and delete them, but if they are in a packfile this doesn't seem simple.

Proposal

Teach Git to garbage collect large binary files from old revisions