[RFC] vim-patch:7.4.268

```
Problem:  Using exists() on a funcref for a script-local function
              does not work.
    Solution: Translate <SNR> to the special byte sequence.
              Add a test.
```

https://code.google.com/p/vim/source/detail?r=1a5ed2626b26a982e307a206572121a557adf709

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I also "refactored" `test_eval.in` to not use registers anymore. Let's see if this ends these scruffy clang asan errors.