practically test the "from borg" importer

[ThomasWaldmann]

I have just added some code to import backups from a borg 1.x repo into a new borg 1.x repo.

borg-import borg -h  # read this!

Importing an archive does:

• for each archive in the source repo
• extract archive to the extraction directory (subdirectory of cwd)
• create a new archive from the extracted data
• delete all files from the extraction directory

This is useful when there is some reason to rebuild the repo:

• use a new AES key (e.g. if your old key might be compromised)
• you can also transfer archives from multiple source repos into a single destination repo
• (add more reasons here)

There is a automated test that succeeds doing this, but more practical tests are definitely needed. Be careful!

[sigmike]

It keeps asking for the passphrase of the 2 repositories. If you have the same passphrase on both repositories, setting BORG_PASSPHRASE works fine, though.

It's pretty slow but there's probably not much that can be done about that.

Otherwise it seems to work fine.