Revert "CPP-987 Make handling of future callbacks play nicely with the predicate guards around cass_future_wait (#559)"

This reverts commit 4a0e4f7.

Author: absurdfarce

src/future.cpp

@@ -189,18 +189,14 @@ bool Future::set_callback(Future::Callback callback, void* data) {
 }
 
 void Future::internal_set(ScopedMutex& lock) {
+  is_set_ = true;
   if (callback_) {
     Callback callback = callback_;
     void* data = data_;
     lock.unlock();
     callback(CassFuture::to(this), data);
     lock.lock();
   }
-
-  // CPP-987 Set this after the callbacks run to avoid unexpected exits
-  // from wait ops due to spurious wakeups
-  is_set_ = true;
-
   // Broadcast after we've run the callback so that threads waiting
   // on this future see the side effects of the callback.
   uv_cond_broadcast(&cond_);