Copy instead of move

[vinjana]

It would be better to have a virtualenv-cp than virtualenv-mv:

• This would simplify the implementation, because no "backup and restore original" logic is necessary.
• Currently, the backup is written close to the source -- a path that may not be writable (it's not for me).
• Move = Copy + Delete -- so copy is more modular. Also, delete is trivial. Furthermore, deletion hurts, if its impossible because of lacking permissions on the source.
• Not that this would be a big issue, but on our NFS the copying of a venv takes quite some time. Doing a backup is unnecessary and thus removing it would also make the script faster.

The only thing that seems to be argument for virtualenv-mv is that the moving the environment is often what people want to do. Why not make a simplified virtualenv-cp and implement virtualenv-mv in terms of virtualenv-cp + delete?