Future rejection should also reject children futures

[othierry]

When a future rejects, the children futures are not rejected. This causes fail blocks of the children future to never be called.

Example

Without children

Future<Int> {
  throw NSError(...)
}.fail { error in
  // This is called as expected
}

With children

Future<Int> {
  throw NSError(...)
}.then { x -> String in // Child future
  return "\(x)"
}.fail { error in
  // This is never called as fail block belongs to the child future
}

[othierry]

Fixed and test case added (The actual test case was wrong and made the error passing...).
Will roll out new version.

[othierry]

Fixed in 2.0.0rc3 and available on cocoapods.