TODO: some notes
common: Some tests for our custome path join
bakcontent: store add: store spec is the rest of the command line
bakcontent-do: NPROCS constant
bakcontent-do: remove dead code
t/t0009: s3 sync test (disabled)
bakcontent: diff command
bakcontent: diff: support restrict to a path; handle new directories
bakcontent: checkout support

Does not overwrite files, only restore missing files.