Updates to const_get

HELLO other Rails-Core people!

I'm trying to push changes to const_get in to ruby-core that will make
our lives easier. I've pushed a branch of Ruby to github. Can you
please check it out to make sure it does what we need?

Here is the link:

  https://github.com/tenderlove/ruby/tree/p2c

When we're happy with the way it works, I'll do the work make sure it
gets merged to ruby trunk.

Thanks!

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