(Wangle) Catch all exceptions in `then() -> Future`

Summary: Saw this while debugging some stuff. Just an oversight, right?

Test Plan: Ran all the tests.

Reviewed By: hans@fb.com

Subscribers: folly-diffs@, jsedgwick, yfeldblum

FB internal diff: D1843016

Signature: t1:1843016:1423704557:d9fdb4b879ab4fcfda54a5fcb16a639df15872b5

folly/futures/Future-inl.h

@@ -192,6 +192,8 @@ Future<T>::thenImplementation(F func, detail::argResult<isTry, F, Args...>) {
             p->fulfilTry(std::move(b));
           });
         } catch (const std::exception& e) {
+          p->setException(exception_wrapper(std::current_exception(), e));
+        } catch (...) {
           p->setException(exception_wrapper(std::current_exception()));
         }
       }