Make the script aware of mdconfig, so it can hopefully run on -CURRENT
as well. This works by selecting "md" or "vn" depending on "uname -r"
output, so we can use the same script on -CURRENT and -STABLE.
Also included minor bugfixes and code cleanup.

Testers welcome, as this code has only been tested on -STABLE
(and for this reason I am doing an immediate MFC).