Should be able to refer to instance folder in websetup

[ali]

This would be really handy for sqlite users, who just want to store the whole thing in a single folder that they can move around.

I can understand why you might not like this, because barely anyone uses sqlite for serious stuff, but it would additionally could be a default setting if the admin really has no clue.

[asmodai]

During the websetup showing the possibility of just using sqlite:///instance/database.db will already help a lot over just sqlite:////absolute/path/to/instance/database.db. Makes it more portable too.

[mitsuhiko]

Done, relative paths in sqlite refer to the instance folder now.