Revert "libutil: remove Pool::Handle::bad"

This reverts commit 792844fb861ea7367ac2316c78fec055363f2f9e.

Change-Id: I3ca208b62edfd5cd1199478f75cd2edf19a364f6

src/libstore/remote-store.cc

@@ -155,6 +155,7 @@ void RemoteStore::setOptions(Connection & conn)
 RemoteStore::ConnectionHandle::~ConnectionHandle()
 {
     if (!daemonException && std::uncaught_exceptions()) {
+        handle.markBad();
         debug("closing daemon connection because of an exception");
     }
 }

src/libutil/pool.hh

@@ -103,6 +103,7 @@ public:
     private:
         Pool & pool;
         std::shared_ptr<R> r;
+        bool bad = false;
 
         friend Pool;
 
@@ -118,7 +119,7 @@ public:
             if (!r) return;
             {
                 auto state_(pool.state.lock());
-                if (!std::uncaught_exceptions())
+                if (!bad && !std::uncaught_exceptions())
                     state_->idle.push_back(ref<R>(r));
                 assert(state_->inUse);
                 state_->inUse--;
@@ -128,6 +129,8 @@ public:
 
         R * operator -> () { return &*r; }
         R & operator * () { return *r; }
+
+        void markBad() { bad = true; }
     };
 
     Handle get()