There are several changes here to avoid uncached method lookups
along hot paths:

* All uses of RubyBasicObject.isBuiltin except for two have been
  replaced with CachingCallSite.isBuiltin. The two that remain are
  for the IO stream wrappers and are not valuable to cache. This
  came up in a profile of RubyKon where Array#any?'s uncached
  isBuitin must be on a hot path.
* All uncached method calls in RubyEnumerable are replaced by
  CallSite.call, including the various callEach forms. These sites
  are localized as much as possible to avoid conflicts, but will
  still churn quite a bit in a typical application that has many
  Enumerable implementers. Long-term we should move Enumerable to
  a Ruby implementation that can be split and specialized.

In addition, in RubyEnumerable all lambdafiable block callbacks
have been replaced by lambdas (fewer class files) and all
deprecated methods moved to the bottom of the file.