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.
Previously, for testing, we were *always* randomizing the build order of
dependencies. That's annoying since it'll make build logs differ randomly
from one run to the next, which could make comparisons harder. However, the
feature is still useful for uncovering hidden dependencies between objects.
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.
