Add constant TAILRECURSION to let a program recognize if tail recursion optimization is implemented
Ruby 1.9 has the possibility to support tail recursion optimization for methods and proc objects. Due to technical problems it cannot be easy implemented for every VM or platform, which will support Ruby 1.9 functionality.
Tail recursion optimization is an implementation detail and not a language feature in general. I propose to supply a constant TAILRECURSION, which will be set to "true" if this feature is implemented, otherwise "false".