* Fairly substantial change.  Instead of creating new globalvariables, then   replaceAllUsesWith'ing any forward references, just use the forward   reference if it exists.
* Fairly substantial change.  Instead of creating new globalvariables, then
  replaceAllUsesWith'ing any forward references, just use the forward
  reference if it exists.

This introduces GetForwardRefForGlobal, which will eventually completely
replace the horrible DeclareNewGlobalValue function.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@14828 91177308-0d34-0410-b5e6-96231b3b80d8

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