Merge pull request #105 in G/fastr from ~ADAM.WELC_ORACLE.COM/fastr:feature/promise_opt to master

* commit 'bb30b492':
  Fixes related to making EagerPromise a final class again.
  Modified option controlling inline caching for promises to allow specifying cache size.
  The EagerPromise class made final again
  Enforce guarantee that if no eager promise evaluation optimizations are used then no eager promises are created.
  A change to enable option-controlled cache-less evaluation of promises.
  Fixed a problem with evaluation of default promises.
  Made a "promised" promise a subclass of "eager" promise to enable "promised" promise stats.