Revert "Simplify variables in compile-stylesheets"

This reverts commit f069acc1dad00797465ecc55d0e21109dfc218e0.

Commit f069acc1 changed the way that the Kuma root was detected in
compile-stylesheets so that output from Stylus would be less verbose.
The particular implementation, however, introduced a bug where the
script could not be run from within its own directory. As it turns out,
there is no easy, portable way to do what commit f069acc1 intended.