With the new "continue" feature on by default, it turned out that
ctrl-c during a build, or a .do file returning an error, would mark a
target as "built" even though it hadn't been. This would prevent
retrying it when you started minimal/do again. Use a temp file
instead.
It's a little tricky: to prevent accidental recursion, we want to
create a file *before* building, but clean up that file when starting
the next session. And we rename that file to the actual .did file
*after* building successfully.
I think this aligns better with how redo works. Otherwise, if a.do
creates a as a symlink, then changes to the symlink's *target* will
change a's stat/stamp information without re-running a.do, which looks
to redo like you modified a by hand, which causes it to stop running
a.do altogether.
With this change, modifications to a's target are okay, but they don't
trigger any redo dependency changes. If you want that, then a.do
should redo-ifchange on its symlink target explicitly.
