BUG: OFstreamCollator: checking for threads. Fixes #659.

src/OpenFOAM/global/fileOperations/collatedFileOperation/OFstreamCollator.C

@@ -430,7 +430,7 @@ bool Foam::OFstreamCollator::write
                 << " using communicator " << comm_ << endl;
         }
 
-        if (!UPstream::haveThreads)
+        if (!UPstream::haveThreads())
         {
             FatalErrorInFunction
                 << "mpi does not seem to have thread support."