largefiles: check hash of files in the store before copying to working dir...
largefiles: check hash of files in the store before copying to working dir
If the store somehow got corrupted, users could end up in weird situations that
were very hard to recover from or lead to propagation of the corruption.
Instead, spend the extra time checking the hash when copying to the working
directory. If it doesn't match, emit a warning, and don't put wrong content in
the working directory.
