Prevent running a rundoc script from deleting the script

[schneems]

Problem

The current way that rundoc works is to build into the local ./tmp dir. This can cause a problem if something in the script calls rm -rf ../.. as it can inadvertently delete the original rundoc script.

One solution

Instead of local ./tmp use Ruby's Dir.mktmpdir to make a temporary directory and do the building in there. Then if they accidentally delete it...no big deal. Once done (success/failure), move the files back to ./tmp.