[Truffle] Fix Kernel#===.
[Truffle] Rename ThreeEqualNode to CaseEqualNode.
[Truffle] Update Kernel#=== tags.
[Truffle] Fix equal?
[Truffle] Fix Array#==.
[Truffle] Implement Bignum#==.
[Truffle] Rename CaseEqualNode to SameOrEqualNode to reflect semantics.
[Truffle] Document SameOrEqualNode.
[Truffle] Get rid of superfluous #=== and #eql? definitions.

* So we match MRI and avoid code duplication.
* MRI still defines #=== uselessly on a couple classes like Fixnum, Symbol and String.
* No more reference to the confusing "three equal".
[Truffle] Tidy up the yield dispatch nodes a bit.
[Truffle] Always split and inline yield.
Cleanup! Removed a bunch of stale FIXMEs.

* Cleaned up some comments.
* Removed some and tweaked some FIXMEs.
[Truffle] Options for inlining yield.
[Truffle] Option for making metaprogramming calls uncached.
[Truffle] Add option for using indirect calls for metaprogramming methods.