Test for ES 5.1 compliance

[s-ludwig]

The amount of changes between version 3 and version 5.1 appears to be pretty small. It would be very nice from a marketing point of view to be able to call this 5.1 compatible, as this is the baseline for modern layered languages, such as TypeScript or Dart.

Getting it to the current version 8 of the standard on the other hand would mean a lot of work and would definitely require a high level of dedication.