Maybe stop setting a umask of 077

Summary

Duplicity sets a umask of 077 for its files, which means that local backup volumes get written as '-rw-------' files.

However, I've had reports of Deja Dup users that have gotten confused by this, when they back up to a drive that is formatted with ext4 and then try restoring on a system with different users.

That new system won't let them read the files unless they first chmod/chown them.

Pitch for why it is unnecessary

• Most backend locations don't respect the umask anyway. From cloud storage (which doesn't have permissions), to sftp (which sets 644 permissions in my test), to backing up to external drives that are FAT formatted.
• Duplicity already offers encryption (by default) if you don't trust the location you're putting your files or are backing up to one of those locations that doesn't have permissions.

I assume the umask was added from a "better safe than sorry" vibe. I see that it has been present since the very first commit 18 years ago!

But, I'd argue that the encryption option is really the "prevent others from accessing these files" solution for users. The umask is a fairly unreliable attempt at doing that.

Possible fixes

I suspect if we take out that umask line, that would be sufficient to use the system umask setting (typically set as 002?), which would give us '-rw-rw-r--' files by default.

I haven't tested that suspicious though, but if you are cool with this change, I can test and make a MR.