Fixed call to undefined function in kv_mutator
Fixed mutator metadata merge

merge_values used to assume two values for the mutaotr list from
metadata at most. Testing has show this is not true as the mutator metadata
lists can be arbitrarily long.
Add unit test for untested mutator merge paths
Merge pull request #692 from basho/bugfix/mw-missing-function-in-mutator

Fixed call to undefined function in kv_mutator