Better error handling for backpus directory setting

[pmario]

see: https://groups.google.com/d/msg/tiddlywiki/rar4JbKs740/zeT2LOSLCAAJ

On another issue, what path can you give fb to tell it to save in an absolute location?

OK I see. Absolute position is forbidden by the browser web-extension API.

    That's not possible (because of browser security concerns) and it's not needed.


Ok, I just realized that I can use ../.. to back out of the current directory. So that works. I don't need to send the backups to a different physical drive. Just one single point where they're not part of the weekly backup plan.

Important for those who don't use a root directory as the browser download dir.

As long as you stay inside the "browser downloads" directory "area" a ../twBackups as the "Backup directory" will work.

BUT as soon as you "leave" the "area" you will see this message in the browser dev Console (F12): save-wiki error: Error: "filename must not contain back-references"

I didn't think about this setting, that's why there is no user facing message atm. So if the setting is wrong there is no warning and NO BACKUPS

I will create a bug-report at github for this.

[pmario]

related to #20