Tries to make copy-on-write semantics upon hard-link copied
directory trees generated with 'cp -la'.
'cow-shell' command invokes a shell session. Within that session,
under the directory cow-shell was invoked, cowdancer will create
a new file when existing i-nodes are opened for write.
Useful for quick scratch workspace and experimentation.
'cowbuilder' command is a wrapper for pbuilder which allows using
pbuilder-like interface over cowdancer environment.