SBT should require a project/build.properties or some other mechanism to avoid assuming any directory is a valid project. #2123
Description
This is more of a nice to have (and I don't think there is an issue on this), but if you start SBT in a folder which isn't a valid SBT project, SBT should either delete the target folder on shutdown, or not create it in the first place
The former I think is more realistic. This just came out because I always have a habit of starting SBT in the wrong place, and it always leaves behind target folders.