Update wrap to correctly return wrapped function arity

This relates to issue (#514)[https://github.com/ramda/ramda/issues/514#issuecomment-62955964]  Have updated the wrap function only in the unminified ramda.js file, as well as added a single testcase.
This would be more at home in a [global .gitignore][1].


[1]: https://help.github.com/articles/ignoring-files/#create-a-global-gitignore