Enable compilation with clang 3.4.

Optimized make_curried_n to instantiate less recursive templates to avoid
hitting clang 3.4's maximum recursion depth. Instantiating a curried function
with curry<N>(f)(args...) and letting curried_fn_n handle the partial
application and recurrying seems simpler, but too difficult for the compiler.
Merge branch 'master' of https://github.com/splinterofchaos/ftl
Merge pull request #12 from splinterofchaos/master

Fix make_curried_n for clang 3.4.