Add an optimization to remove ref temps when possible

This changeset makes inlineFunctions remove reference temps when possible. "Possible" is defined as any call that is a primitive or only contains primitive calls. While not perfect, this does remove ref temps for simple things like =, +=, *=, etc.

test_nested_var_iterator3 has been turned into a bug future in the pull request. A limitation in copy propagation was exposed by my changes, Tom is aware of this and said he will look into it. 
How so? Isn't this preventing ref temps from being removed? 

If you have 

func() {
  func2()
}

and they both have ref temps that can be replaced, won't you be preventing ref temps from being removed from func()? (assuming that once func2() has been inlined, func() has no other non-primitives)