This is fork of Microsoft DLR source code. The original code was published at
http://dlr.codeplex.com/ which had the code used for .NET 4.0
System.Linq.Expression public API. Since them the code was migrated to
https://github.com/IronLanguages/main but it no longer has the goal to offer
compatible System.Linq.Expression API and we cannot use some part of it.

We want to have minimum local changes. Importatant changes need to be marked
using easily recognizable marker (like MONO_INTERPRETER) for easier merging.