adopt-project.py: check names, and execute refuses before the work directory is made, a plan whose source: or legs: is not a mapping or whose allow_empty_legs: or paths: is not a list of what plan writes, and asks the same first of a pins: that is not a list, so a number or a boolean in any of the four no longer ends both in a traceback and allow_empty_legs: code is no longer read as four legs (#386) - #435