Initialize CoffeeScript >= 1.7.0 for both directory and file loads

Commits b9e455b3b9bea293e0beb1d850df9dc1587148b5,
df5359bb24fd013043aa05c10264e9267e9ea5fb, and
55093f141cd61a2481c6d52b11b07993613ae17d introduced changes to register the
CoffeeScript compiler as required by CS >= 1.7.0.  Unfortunately the
registration only handled directory loads and not file loads.  This commit
centralizes the compiler registration in the _requireCoffee function so
that it is always called.  This problem was breaking Jake with Jake 0.7.9,
CoffeeScript 1.7.1, and Node 0.8.26.