[Truffle] Move lexical scope state to the ParseEnvironment, a per-parse TranslatorEnvironment.
[Truffle] Document logicalClass VS metaClass.
[Truffle] Passing spec.
[Truffle] Fix no method NameError message.
[Truffle] Another passing spec.
[Truffle] Fix #is_a? and #instance_of?.
[Truffle] Remove tags for a few passing language specs.
[Truffle] New failing spec.
[Truffle] Fix transcoding convert specs.
[Truffle] Implement a couple things to make MSpec auto add tags work.

* Fix order of methods.
* File#exist? should just check existance, not file type.
* Will not work if the directory does not exist, but that sounds rather rare.
[Truffle] Move Array guards ro ArrayGuards and use ImportGuards.

* Remove the duplicating classes Yielding[Type]CoreMethodNode.
[Truffle] Fix variable type and name.
[Truffle] Move Hash guards in HashGuards and fix the build.
[Truffle] Lookup DATA on Object, not its singleton class.
[Truffle] Keep ENV in CoreLibrary since most usages will access it directly.
current MRI prepend implementation
adding missed file
fixup! adding missed file