Yeah, sorry emails have been very problematic recently so I am just polling on this JIRA
Indeed, Spark relies on mapred home to pick up Input/Output format classes. Things may have changed more recently but I think that's still the case, which is why we need it.
As far as compute-classpath.sh goes, my original testing revealed that we needed it. So, it's there. We can look more into if it's possible to remove it as an follow-on JIRA (which may or may not get resolved by Bigtop 0.8). Sounds like you are ok with that since you mentioned "Other than that +1. Please commit."
So, in spirit of marching towards the release, I will commit this but please yell at me if there is anything else!