Add tailrecursive annotation that makes the compiler check if a given function is tail recursive

[inoas]

https://www.youtube.com/watch?v=YKwBBe3FlAM#t=17m12s at 17m12 shows the feature in Scala.

[inoas]

I hope we can have this as this allows a programmer to state his intention and then the compiler to tell the programmer that s*he is wrong.