Get rid of "evilsSeed is not defined"

This `ReferenceError: evilsSeed is not defined` is driving me crazy. I can always reproduce it by simply shift+reloading a page in my local Wikibase Repo. This is a huge pain when debugging. I still have no idea what causes it. It could be the garbage collection going crazy.

This patch:
* Replaces evil `eval` with `new Function( ... )`.
* Adds a `typeof` check.
* Adds a fallback to the original (unnamed) function.