Print something better than [Object object]

If we ever load javascript (uniload load or package.js parse) outside of
a buildmessage job and there's a syntax error, FancySyntaxError gets
thrown instead of properly processed. Now, we shouldn't do that (we
should only load JS inside a buildmessage job!) but our codebase isn't
currently up to that standard, so at least ensure that there's some
level of useful syntax error (albeit with an ugly internal stack trace
attached) in this case.