Back out "cut references to exception_wrapper::hasThrownException"

Summary: Also backed out D28276400 (https://github.com/facebook/folly/commit/b24643035fb8778b87feefdb3a365c06583ce53f) because it has a dependency to D26331579 (https://github.com/facebook/folly/commit/aa7f74aaf68ab0a7eb834f49a864c277dbe5fe09)

Reviewed By: lhuang04, JunqiWang

Differential Revision: D28309181

fbshipit-source-id: 0e04e00c59d497290aa0067177a51fe1cfc5e144

folly/ExceptionWrapper.h

@@ -394,10 +394,12 @@ class exception_wrapper final {
   ~exception_wrapper();
 
   //! \post `!ptr || bool(*this)`
+  //! \post `hasThrownException() == bool(ptr)`
   explicit exception_wrapper(std::exception_ptr const& ptr) noexcept;
   explicit exception_wrapper(std::exception_ptr&& ptr) noexcept;
 
   //! \pre `ptr` holds a reference to `ex`.
+  //! \post `hasThrownException() == true`
   //! \post `bool(*this)`
   //! \post `type() == typeid(ex)`
   template <class Ex>
@@ -407,6 +409,7 @@ class exception_wrapper final {
 
   //! \pre `typeid(ex) == typeid(typename decay<Ex>::type)`
   //! \post `bool(*this)`
+  //! \post `hasThrownException() == false`
   //! \post `type() == typeid(ex)`
   //! \note Exceptions of types derived from `std::exception` can be implicitly
   //!     converted to an `exception_wrapper`.
@@ -419,6 +422,7 @@ class exception_wrapper final {
 
   //! \pre `typeid(ex) == typeid(typename decay<Ex>::type)`
   //! \post `bool(*this)`
+  //! \post `hasThrownException() == false`
   //! \post `type() == typeid(ex)`
   //! \note Exceptions of types not derived from `std::exception` can still be
   //!     used to construct an `exception_wrapper`, but you must specify