Circumvent "local function" bug in Xcode 6 beta 6

Removes the compiler error:

    (...)/swiftz_core/List.swift:91:16: error: cannot reference
    a local function from another local function
Merge pull request #98 from pyrtsa/fix/beta6-cannot-reference-local-function

Circumvent "local function" bug in Xcode 6 beta 6