[IR] Bug fix in AliasInstr -- "method_added" callback was missing

* Fixes a rubyspec failure from the recent update.
[Truffle] Temporarily restore separate version of RubySpec for Truffle.

Just until we can get the new specs running in Truffle.
Tag out 4 final IR errors vs AST interp
[Truffle] Move type check of $~ into a separate node.
Merge remote-tracking branch 'origin/master' into new_transcoder