Redirect messes up system.js error reporting

[codefrau]

system.js tries to remove itself from error stack.
In addToError() it looks at $__curScript, which is
https://lively-next.org/lively.next-node_modules/systemjs/dist/system.src.js
(derived from the src tag of its own script element) but the stack trace has
https://lively-next.org/lively.next-node_modules/systemjs/0.19.47/dist/system.src.js
because of the HTTP/1.1 301 Moved Permanently server response.