DumboJetEngine

I have a working implementation of this, that also adds some extra tiny features. It appears to work for the queries I tested it on, but I will need to...

@Xtansia Is it OK if I send, in one commit and one PR, the implementation for this issue ( #446 ), #380, and #375 ?

@Xtansia OK. Done. If you can review and merge the two small PRs I have just sent, so that I can resolve any conflict for the 3rd, it would be...

Oh.... Cancel that. It did it only once. Now I can't reproduce it any more... :o I had tried reloading the page many times, but it didn't help. Probably something...

I have tried out a fix that seems to work without breaking the existing tests. I am not an expert on the internals of Mapster, but this is the fix...