Use set -e and trap rather than "successfully"

Behavior should be identical. set -e will cause any failing command to exit
and the trap will output "failed" on stderr, like successfully used to.

I did not (yet) build the new complete scripts, the echo's in bin/build 
print literal newlines on my system (because of the bin/sh shebang). I 
have a fix in my other PR which I'll wait for and update this PR after.