The problem is that redo-ifchange has a different $PWD than its
sub-dependencies, so as it's chasing them down, fixing up the relative paths
totally doesn't work at all.
There's probably a much smarter fix than this, but it's too late at night to
think of it right now.
atoi() was getting redundant, and unfortunately we can't easily load
helpers.py in some places where we'd want to, because it depends on vars.py.
So move it to its own module.
It used to say:
redo: t/all
redo: hello
and now it says:
redo t/all
redo t/hello
ie. there's no colon, and the path is intact. That means if the build
fails, you can cut-and-paste 'redo t/hello', add a -v, and try to debug
what went wrong.
